Do I need to get a motherboard with PCIe 3.0 for a 3.0 graphics card, or will it be fine if I just get a motherboard that only has 2.0? I know PCIe 3.0 cards are backwards compatible with 2.0, but is there any advantage to 3.0 over 2.0?
pcie 3.0 16x is double the bandwith of pci 2.0 16x, it might make make a difference in the future with sli 980s and tripple 4k monitors but right now even the performance difference between pcie 2.0 16x and 8x (half the lanes/bandwith) ranges from 0% to margin of error. I wouldnt worry much about it.
Doesn't make a difference... Even the most powerful current GPU's can't completely saturate PCI-E 2.0.
Don't worry about it. Unless you're going to stick a 7990 into a PCI-e 2.0 8x slot, you will not hit any performance degradation.
you will only see a difference in performance if you saturate all the lanes and have something that is dependent on bandwidth.
Also, it only effects single card configurations (as the current PCIe 3.0 spec only allows 8x/8x CF/SLI which is theoretically equal to PCIe 2.0 16x/16x).
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Yup, if the stars align you might get a 2 or 3 extra fps.
This is more of a function of the CPU you're using than the spec. Intel Ivy Bridge-E processors have 40 PCIe 3.0 lanes so you can easily run 16x/16x or 16x/16x/8x or 16x/8x/8x/8x at 3.0 speeds if you wanted.