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Questions about crossfiring 7850's and PCIe speeds.

Last response: in Motherboards
February 21, 2013 5:54:33 AM

I have an Asrock H77 pro 4 mvp, gigabyte 7850, and an i5-3470 on the way for my new build. The manual for the h77 says it has one PCIe 3.0 x16 (PCIe 2.0 x16) slot, one PCIe 2.0 x16 (PCIe 3.0 x4) slot, and one PCIe 2.0 x1 slot. Does this mean that since I will be using an ivy bridge cpu that the first two slots will be running at PCIe 3.0 16x/4x? Would getting another 7850 down the line then be a waste of money, or, even if the second card isn't being used 100%, would the performance gains be enough to justify it? Could the different speeds actually cause performance issues, and end up being worse than just the single card? I've been having trouble finding reliable information on this as there seems to be some disagreement among people and little in the way of actual benchmarks and things, so thanks for any help in advance.
February 21, 2013 11:42:41 AM

Presciently, in CrossFireX mode the cards will run 16x/4x and you don't want that ...16x/8x is fine but 4x is not good. So you have two options: 1) Buy a new z77 motherboard so you can CF 16x/8x or 2) sell your 7850 and buy high end video card instead of CF
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February 21, 2013 11:46:34 AM

correction z77 support 8x/8x
February 21, 2013 2:05:34 PM

Thanks for the reply's. It's funny though, because I got two reply's, and they disagree with each other. You say small performance loss, and I'm ok with that, but the other guy says don't do it. If the only loss is about a 10% difference like those benchmarks show, then I think I might go ahead and do it.

February 28, 2013 3:58:51 PM

The main reason is microstuttering. You will get it more with 16x4 than with 8x8 or 16x16