Will a Core i7 920 @ 3.2 GHz bottleneck the 5870 in triple crossfire x

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ryan2258

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Hello,
I am currently running two HD 5870's in crossfire and I was wondering if my CPU would limit any possible gains of adding a third 5870 for triple crossfire X. I just read a review that shows some pretty significant difference when adding a third card but the reviewer had the new 6 core intel chip (the 980x). The reviewer left the CPU at stock clocks. If I upped the OC of my CPU would I see similar gains?
 
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megamanx00

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Sep 3, 2008
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Just depends on the game as to if you will see an increase with a 3rd card. Granted some of them will be limited by your CPU if you have 3 5870s, but others not so much. Pushing your CPU a little more will of course help with that. If you can get your CPU to about 3.8GHz then there would be little benefit to moving to a 6-core 980X right now.6
 
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Talon

Talon

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Agree with Shadow, at 3.2 you might be bottlenecked in some instances but there have been more than 1 article on the "net" that have mostly agreed that 3.6Ghz is the "sweet spot" for getting the most out of your system for the cost/heat/efficiency etc.

I'd say OC to 3.6Ghz if you can and you should be just fine. The 6-core is at the moment overkill unless you have money to burn. The cost for the extra you will actually see is negligible in games for now.
 
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bystander

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Dec 9, 2009
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Check this comparison with crossfire 5870's at different i7 920 clock speeds. It shows the effect of different resolutions as well. http://www.xbitlabs.com/articles/video/display/radeon-hd5870-cpu-scaling.html

In situations where overclocking the CPU didn't increase FPS, those are situations were Trifire would increase performance. In situations where overclocking the CPU continue to increase performance, it's likely that game is CPU bottlenecked.

It does appear that the i7 920 will bottle neck the system in many situations.
 
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ryan2258

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I'm using the asus p6t mobo. I do my gaming at 2560x1600 resolution so I need all the graphics horsepower I can get. I just replaced my 1010w OCZ PSU with a modular 850w Cooler Master Silent Pro. I just read an article that shows that the 5870 in tri crossfire only consumes 577 watts http://www.pcper.com/article.php?aid=796&type=expert&pid=8 . Can my new power supply handle a third card? It's got a single 12v rail with 66 amps.
 
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shadow187

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Sep 16, 2009
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Yes, each 5870 won't use more than 16A at load, comes out to 48A, which leaves you 18A or 180Watts for CPU oc'ing.

hd5870_power.png


Your 5870 won't even go above 120Watts while normally gaming.
 
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shadow187

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Agreed. That's the reason I want ATI do up the power usage to gain more performance. If they scaled up their power/performance, they would absolutely kill.

The 5770 doesn't use more than 60Watts, the 5670 doesn't use more than 25 (Crysis). Love xbitlabs.
 
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ryan2258

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Ya I'm really liking my new ATI cards. They run really cool, quiet and efficient. Its surprising that my 850w power supply can easily power three 5870's. My old 1010w PSU struggled with the three gtx 260's I had previously.
 
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ryan2258

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Nope. Just dreaming at this point. Not to get off topic but I've been saving for the new Asus G73JH laptop. Do you guys think its worth buying. I currently own Asus' previous gen gaming laptop the G50vt-x5.
 
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