What would happen to your gaming performance if instead of running in SLI in x16/x16, you instead ran in SLI at x8/x8? [H]ard|OCP answers that question in their latest graphics article. The answer was, to me at least, somewhat surprising. It appears that PCIe bandwidth, at least for games, is not that big of a deal. I wonder if the same holds true for GPGPU applications?

If you are running on a 30″ display at 2560×1600 or below, an x8/x8 SLI or CFX configuration will perform the same as a x16/x8 or x16/x16 configuration. The only time that you should even be slightly concerned about running at x8/x8 is when you move up to a multiple display setup. When we pushed the GTX 480 SLI at 5760×1200 we saw up to a 7% difference in performance between x8/x8 and x16/x16, in favor of x16/x16, but that was in one game only.

via Introduction – GTX 480 SLI @ 2560×1600 – GTX 480 SLI PCIe Bandwidth Perf. – x16/x16 vs. x8/x8 | [H]ard|OCP.