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PCI-E 16x SLI vs 8x SLI

post #1 of 17
Thread Starter 
Ok so I have a new rig that I am building....It has 2 GTX 580 Lightnings and the way my motherboard is set up...the 2 16X slots on the mobo are spaced where the cards are right on top of each other.

This causes the top GPU to be about 15 degrees hotter than the bottom one. Now I can space them out, however I would have to utilize a 16 X and a 8X slot...Which would cause them both to run at 8x.

If I do this then it will be much better for temps, however what kind of performance hit will I take???
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The Gibson
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post #2 of 17
IIRC, it's a 2-4% drop in performance...won't even notice it unless you're benching.
post #3 of 17
Yep, completely negligible even if you're benching and even then it's pretty negligible. The only time it makes a difference is if you're running one card on 4x, and there have been some reviews indicating that even then, it's negligible unless the cards are being run at ultra high resolutions.
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post #4 of 17
Thread Starter 
Quote:
Originally Posted by mongoloid View Post
IIRC, it's a 2-4% drop in performance...won't even notice it unless you're benching.
ok thanks...Yes I will be benching...however I got these lightnings to OC them....If I have a ton of heat going on then I cant really OC them like I want to...lol...

Maybe with OC to 950Mhz I will make up for the performance loss...Cheers mate...
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post #5 of 17
Try benching with the x16 slots populated and run open box?
post #6 of 17
The performance difference of a 16x slot vs an 8x slot really isn't discernible.
post #7 of 17
Quote:
Originally Posted by Strider_2001 View Post
ok thanks...Yes I will be benching...however I got these lightnings to OC them....If I have a ton of heat going on then I cant really OC them like I want to...lol...

Maybe with OC to 950Mhz I will make up for the performance loss...Cheers mate...
Bench em open case, with a piece of tubing wedged between the cards to help them breathe. run em in your case at 8x-8x.
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post #8 of 17
Performance wont be hurt too bad as others stated. If its an issue for you why not water cool them and stick them in the x16 slots? Under water you will be able to overclock better anyways.
post #9 of 17
I think a GTX 580 performance exceeds the bandwidth of PCI-e 2.0 x8 (which is equivalent in bandwidth to PCI-e 1.1 x16), so there might be an issue. Whether you'll see it in real gaming performance, I can't say.

Someone else asked the same question here: http://www.techpowerup.com/forums/sh...d.php?t=137861

And there was a study done with a GTX 480 here: http://www.techpowerup.com/reviews/N...Scaling/1.html

But no hard numbers for a GTX 580 set-up. The admin that did the other review on the 480 said that he'd do one on the 580, but it looks like it hasn't been done yet.
    
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post #10 of 17
Don't think Lightnings have blocks available currently.
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