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Minimum CPU needed to not bottleneck Crossfire 7950s?

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August 25, 2013 10:28:24 AM

Hi. What is the minimum CPU I would need to not bottleneck crossfire 7950s?
August 25, 2013 11:17:39 AM

4670/k Would be a good bet or you might get away with a fx 6350
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August 25, 2013 11:36:59 AM

A i5 3570K or a FX-6300 or better would be just fine. I have a FX-8120 based rig with a Sapphire HD 7950 Crossfire setup and it runs all of my games great. I run that rig on a Eyefinity setup with 3 27" monitors at 5760x1080 and with the latest beta CCC drivers it runs very well. As far as AMD CPU's go I have not used a FX CPU lower than a FX-8120 so I can't really say much about lower class CPU's.

As for intel I have a i5 3570K and have tested my Sapphire HD 7950 setup on that rig and found no problems on it either. There again the i5 3570K is the lowest CPU I have tested with intel.
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August 25, 2013 11:38:44 AM

Without knowing your resolution, and what games you are talking about, there is no way to know.

You might also let us know at what FPS do you want to play at, as you may be bottlenecked, but not care if you have XX FPS.
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August 25, 2013 12:01:26 PM

Thanks for the replys guys. I'm thinking about getting the 4670k as the price differences between all these CPUs are marginal and I figure I should get the best but I have some questions.

I've looked at the best CPU for money page. Their recommendations are as follows.
I3- 3220 for $120.00. Budget gamers pick. Do you think this CPU would cause bottlenecks?
i5- 3350P for $180.00. High performance gamers pick. I've never overclocked a CPU and have no clue how to do it but I think it would be nice to have the option available to me should the need arise. They say here that if you don't plan on overclocking then there's not much need to go above the i5-3350P.
i5- 3570k for $220.00 overclocking gamer's pick. They don't have the 4670k listed here and I've read someone on here that there's not much difference between the 3570k and 4670k. But then the price isn't much different either.

So out of all these the only one that's really worth mentioning as far as savings goes is the i3. It's about 100 bucks cheaper. But if there is any chance It will cause bottlenecks I won't go for it. The 3350P is at best 60 bucks cheaper than the 4670k so I think it would be better to just spend the extra 60 and get the better CPU with overclocking capability.
What's difference between the 3570k and 4670k? If I were to get one of these I'd probably just spend the extra 20 or 40 bucks or w.e it is to have the overclocking option available.

Now on to the i7. I see here that they don't recommend anything above the 3570k because of diminishing returns. But they also say this...

The Core i7-3770K only enjoys a 100 MHz-higher clock rate than the Core i5-3570K. Its real advantage is an extra 2 MB of L3 cache and Intel's Hyper-Threading feature. Neither of those extras have a big impact on gaming, but there is a small number of titles (like Crysis 3) that take advantage of extra resources, translating to a performance increase. Having said that, this is still rare, and the Core i7-3770K will be more useful to power users who want better performance in well-threaded apps, in addition to the best frame rates in games.

Well how much of a performance increase are we talking here? Because I do play Crysis 3 and I'm assuming if this game can benefit from the i7 then future games may very well benefit from it also.

As far as AMD CPUs go, I've been told they are not so good. The guy at the computer store says he can't stand them and that Intel is the way to go.
I don't see a huge price difference between the two brands either.
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August 25, 2013 12:12:19 PM

I play at 1080p. My main thing is MMORPG. Currently playing Star Wars the old republic but I plan on playing future title. And then I play a lot of shooters like Crysis, Metro, BF4 when it's released. And I hate anything below 60fps :) 
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August 25, 2013 12:22:33 PM

Pavel Pokidaylo said:
I play at 1080p. My main thing is MMORPG. Currently playing Star Wars the old republic but I plan on playing future title. And then I play a lot of shooters like Crysis, Metro, BF4 when it's released. And I hate anything below 60fps :) 


Playing at that resolution, you'll be bottlenecked a lot, especially when playing MMORPG's, which are fare more CPU intensive. Just get as fast of a CPU as you can.
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August 25, 2013 12:30:50 PM

Yep. I have the i7 920 right now and CPU-Z shows that the core speed is over 3500mhz. I never OC'd it, I guess they did it at the factory. In 16man raids or warzones where there are lots of people casting spells and abilitys my FPS plummets to terrible levels. Sometimes as low as 10fps. Going from a 6770 to a 7950 made absolutely no difference so it must be the CPU.

Crysis 3- with one card I see the GPU usage at 100% pretty much all the time. But when I added the second card I saw no increase in fps at all and the GPU usage of the second card was way lower. This happened with pretty much every game I tried on the Crossfire setup.

I've also been bottlenecked with just the one card in many games. The worst is SWTOR of course. But many single player games also show bottlenecks. Hitman-Absolution, Withcer 2 are a couple of the games that are being bottlenecked.

I brought my cards to the computer store and we put them on a motherboard with an i5 3340 I think it was (can't remember the exact model).
We booted up FarCry 3 and it was amazing. Constant 60-70fps. It would dip occasionaly into the 50s and sometimes high 40s but I attribute that to the game or maybe Crossfire. Besides those occasional dips it was great. Max settings with 4XMSAA and the game looked gorgeous and ran very well. I was very happy to see that my cards aren't garbage.

So which CPU do you recommend? I5- 4670k?
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August 25, 2013 1:26:02 PM

If you got an aftermarket HSF and OC'ed that CPU to near its limits, it would help a lot. i7 920's at 4Ghz, are very comparable in performance to i5 3500k's at stock. I doubt your CPU-Z reading is exactly accurate. Also, what is the memory in that thing?
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August 25, 2013 2:10:24 PM

8gig Gskill 1600xmp. 2 sticks of 4gig each.

That's why I'm kinda bummed that my i7 920 isn't performing as well as others. I see you have an i7 920 @ 4.0ghz. Do you see any bottlenecks in games with it?
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August 25, 2013 2:17:08 PM

Pavel Pokidaylo said:
8gig Gskill 1600xmp. 2 sticks of 4gig each.

That's why I'm kinda bummed that my i7 920 isn't performing as well as others. I see you have an i7 920 @ 4.0ghz. Do you see any bottlenecks in games with it?


I see occasional bottlenecks, but so does everyone else. However, they aren't anything like you describe. I asked about the memory, because you are losing performance with 2 sticks. The 920 uses triple channel memory, and works best with 3 sticks or ram.
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August 25, 2013 3:01:40 PM

Yep I've been told that it works best with 3 sticks but they said they don't think I'm realy losing much performance if any from having 2 sticks.
Do you know what your CPU scores on the physics test in 3dmark11?
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August 25, 2013 3:04:01 PM

Also I'll probably get the 3570k or 4670k but do you think I should get an i7 instead? Or will the i5 suit my needs?
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August 25, 2013 4:01:45 PM

Bystander still there? Was hoping you could tell me if I'd be better off getting an i7 over the i5-4670k. And about that dual-channel vs triple-channel performance thing, how much am I missing out on by having dual-channel?

Also I ran Firestrike test and got this result. Graphics score- 7779, Physics score 7910, Score- 6718. Is this normal? I had the 7950 overclocked at 1100mhz on the core and 20% on the slider. Didn't touch the memory.
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August 25, 2013 4:57:23 PM

My 3Dmark11 score in physics is 8485, though I'm not sure if that was at 4.0 Ghz, or just a touch lower.
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August 25, 2013 5:48:29 PM

Bystander I guess that would make sense since we have the same CPU and yours is overclocked more. When I ran 3dmark11 (performance) last time I got only 5300 and then with two cards it was 5000. I get much better results in FireStrike but that doesn't matter because I'm still getting massive bottlenecks in games. I guess a good physics test in FireStrike doesn't mean anything when it comes to real games.

And thanks for the reply Byogamingc. Good to know what the minimum would be.

So would you guys suggest I go for an i7 or just get the i5 4670k. I mean do you think it would make a big difference, maybe not in current games but future titles?

And does anyone know exactly what kind of performance loss I'm looking at from having Dual-channel instead of triple-channel ram with my i7?
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August 25, 2013 5:54:17 PM

Pavel Pokidaylo said:
Bystander I guess that would make sense since we have the same CPU and yours is overclocked more. When I ran 3dmark11 (performance) last time I got only 5300 and then with two cards it was 5000. I get much better results in FireStrike but that doesn't matter because I'm still getting massive bottlenecks in games. I guess a good physics test in FireStrike doesn't mean anything when it comes to real games.

And thanks for the reply Byogamingc. Good to know what the minimum would be.

So would you guys suggest I go for an i7 or just get the i5 4670k. I mean do you think it would make a big difference, maybe not in current games but future titles?

And does anyone know exactly what kind of performance loss I'm looking at from having Dual-channel instead of triple-channel ram with my i7?


The scores between 3Dmark and 3Dmark11 can't be compared, so basically, your score is low enough to think it is still at stock. 5300 vs 8500 is a huge difference. I'd either update the CPU, or get a good aftermarket HSF and OC that baby. I keep seeing benchmark comparisons with the 920, and when OC'ed to 4ghz, they still compete with todays chips.

Also, you can't compare the physics scores of an i7 to an i5, because hyperthreading really helps 3dmark/11 physics scores, as it will use all the threads available, but in most games it isn't used much.

I wouldn't expect dual vs triple to make that big of a difference, but it may make some difference.
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August 25, 2013 8:31:13 PM

Someone just informed me that the difference between triple and dual would be less than 3%.

I've seen some i7s get ridiculous physics test scores in 3dmark11 but that's far from a deciding factor for me. I found an earlier post I made with a 3dmark11 result and it had my physics test at over 6000. Now it's lower in 3dmark11 for some reason.

Also I was told that since my motherboard is OEM, It won't allow overclocking. But then I was also told that even though it's OEM it will allow it.
Now CPU-Z, the XSBench on realtemp, and 3dmark all show that my CPU is overclocked to about 3.5ghz.
I'm going to try and find out if my motherboard would allow overclocking right now. If it does maybe I'll do that but I've never done it before and have no clue what I'm doing. Someone linked me a guide to doing it and said it was the easiest and best guide they've used yet but when I looked at it it was like 10 pages long lol.

At any rate, I'm probably just going to get a new CPU. most likely it will be the i5 4670k unless someone tells me that I may see a significant increase in performance in games by going with the i7 instead.

I'll also need a motherboard with good spacing between the PCI slots. As well as a new case, I'm thinking full tower since I want an ATX motherboard instead of a micro ATX and a full tower would probably have more room to work with.
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February 20, 2014 12:36:10 AM

bryonhowley said:
A i5 3570K or a FX-6300 or better would be just fine. I have a FX-8120 based rig with a Sapphire HD 7950 Crossfire setup and it runs all of my games great. I run that rig on a Eyefinity setup with 3 27" monitors at 5760x1080 and with the latest beta CCC drivers it runs very well. As far as AMD CPU's go I have not used a FX CPU lower than a FX-8120 so I can't really say much about lower class CPU's.

As for intel I have a i5 3570K and have tested my Sapphire HD 7950 setup on that rig and found no problems on it either. There again the i5 3570K is the lowest CPU I have tested with intel.


Pretty sure an FX-6300 bottlenecks a single 7950 in some games if I'm not wrong. But an i5-3570K is enough for sure.
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