Crossfire questions for the confused

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old_raist

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Aug 5, 2013
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Hello,
I have recently upgraded to the awesome (IMO) Asus PA278Q 2560x1440 display thanks to a fortuitous work requirement, but now I wonder if i need a 2nd HD7950 to get the most out of it when gaming? I play a bit of everything, and like the idea of squeezing the most out of this display.

With the release of Catalyst 13.8, it seems that AMD have started to address the previous issues (if not completely fix them yet), but I could just spring for a single GTX780 instead to eliminate any CF/SLI issue.

So, my questions are:
1. 2nd HD7950 or 1x GTX780 @ 2560x1440?

2. Is the power draw of CF/SLI when doing non-gaming tasks (PS, AI, office apps etc) too high to make it a viable option?

3. Do I even need to worry about either option when i can just turn down the eye-candy instead? (but I do love eye-candy)

All advise greatfully recieved.
Thanks in advance.
 
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What is the rest of your specs? (cpu and psu specifically)

1. Two 7950s will be much more powerful than a single 780 in games that use it correctly.
2. The second gpu's clock is 0 (at least for me) when not gaming so there is virtually no power draw. Crossfire is only enabled when you run something in full screen.
3. That's a matter of opinion. I can't answer that for you.

I have 7870CF and a 2560x1440 monitor so I may have some good advice for you. For starters the driver; I installed 13.8 over the weekend. So far I found one bug. I went to watch a youtube video in full screen and my main monitor got all artifacted, but my secondary was fine. It has never happened before so I blame 13.8 for that.

As far as smoothness goes I notice...
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wanderer11

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Jun 11, 2012
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What is the rest of your specs? (cpu and psu specifically)

1. Two 7950s will be much more powerful than a single 780 in games that use it correctly.
2. The second gpu's clock is 0 (at least for me) when not gaming so there is virtually no power draw. Crossfire is only enabled when you run something in full screen.
3. That's a matter of opinion. I can't answer that for you.

I have 7870CF and a 2560x1440 monitor so I may have some good advice for you. For starters the driver; I installed 13.8 over the weekend. So far I found one bug. I went to watch a youtube video in full screen and my main monitor got all artifacted, but my secondary was fine. It has never happened before so I blame 13.8 for that.

As far as smoothness goes I notice no difference from 13.6 to 13.8. The only games that ever felt unsmooth were Metro2033 and Skyrim. I just forced vsync/triple buffering with d3doverrider and it was fine.

The best was to determine if you need a more powerful gpu at the moment is what games you play. I spend most of my time on indie games, but play the occasional AAA game. The only reason I got my second 7870 was it was on sale and came with a bunch of games I wanted.

If you have any questions let me know, since I have a very similar setup to yours.
 
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coozie7

coozie7

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Jun 2, 2007
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The power supply will need to be strong if you decide to go CF, make sure it's up to the job.
First I'd play the games and see how it goes, you'll need to turn some things down at that res: AA, smoke, fog, shadows and top end lighting effects like sun rays hammer the framerate the most.
1: The GTX770 is nearly as fast for a whole lot less and I have never liked multi-GPU setups...'Nuff said.
2: It'll turn one card practically off and downclock the other at idle/light use, so yes, it's viable.
3: See above.
 
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old_raist

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Aug 5, 2013
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Thanks Coozie & Wanderer,
That was my first post and I got helpful answers almost immediately, what a great community!

My Specs:
CPU: i7 920 (X58) @ 3.8oc
Ram: 6gb Corsair XMS
PSU: Corsair HX850
GPU: Sapphire HD7950 Boost
Display: Asus PB278Q 2560x1440

I know my system is a getting on a bit, but other than the original GPU (GTX275), nothing else has given me a reason to update since 2009 when I built it.

I generally play anything 'good', AAA titles through to indie ones, the only games I don't get into are the competitive online shooters and any RTS that isn't Homeworld.

Now that I know about the low power state for non-gaming activities, I will probably go with the 2nd HD7950 since its a cheaper upgrade path until I build a new system early next year.

Thanks for your help guys, and I would be very interested if you have any other comments/advise.
 
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wanderer11

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I'm not too familiar with the i7-920 (that was before I got into computers), but my 3570k holds back my setup a little bit at stock. For example, on Crysis 3 when I have an fps dip my gpus were both used around 90% and my cpu had 2 cores maxed out with the other 2 probably at 75%. That's the ony game I have noticed my cpu maxed out. The extra 4 threads on the cpu would probably help to alleviate that though.
 
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coozie7

coozie7

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Jun 2, 2007
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@ old_raist: Thanks, pal, I feel so much better, sitting here typing on my old i5 750 machine ;).
Dual 7950s' are really going to run like lightning and their large memory buffers help with eye candy at such a high resolution so +1 BigMack70 for the CF suggestion.
Just to clarify what BigMack70 said later: As the monitor resolution increases the workload on the graphics system goes up accordingly, BUT the CPU workload does not increase anything like as quickly. These old-I'm not going to let you forget that-chips are not as fast as the current gen so it will hold back Crossfired 7950s', but just a bit.
One last point, check the card spacing on the motherboard, it's common to find the top card too close to the bottom one which can lead to heating issues, and the last thing you want to do with a 7950 is starve it of air (mine's all alone in a well ventilated case and can still hit 75C under Far Cry 3).
 
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wanderer11

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I play at 2560x1440 too. I really need to get around to making a signature.
 
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old_raist

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Aug 5, 2013
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Thanks to everyone for their help, I am going to get that 2nd 7950 today before i read another article/forum and second guess myself!

Coozie7 made a good point, my 2nd PCIE_16 slot is only 1-2mm below the fans of my current card, which has me thinking about heat.

Q. Is it better to use the x16 slot and just crank the case fans, or use the x8 slot for better thermals/less lanes
?

FYI - when using current 7950 (1175/1650) @ 2560x1440, my highest temps are ~70deg on Crysis 2, Far Cry 3, Bshock Inf etc. Generally sits around ~60deg for most graphics intense games. Everything set to Ultra if possible.

FYI.2 - My mobo is a ex58-ud4p if that helps anyone?

 
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old_raist

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Aug 5, 2013
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Thanks again for all you help guys,
Got the 2nd card installed just now with no Post/Windows issues, time to see what they can do.
The only problem I can see is that I couldn't fit the 2nd card into the x8 slot due to the psu getting in the way, so I have put it in the 2nd x16 slot and will have to watch the temps for a while.

If I could have chosen 2 solutions, Coozie7 would have got one as well, both guys were really helpful.
 
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