Does PCI-e bandwidth effect performance with SLI/ Crossfire?

[Gilly]

http://www.hardocp.com/article/2010/08/16/sli_cfx_pcie_bandwidth_perf_x16x16_vs_x16x8/1

Basically a comparison using SLI and Crossfire of 16x/16x lanes against 16x/8x lanes.

In simple terms, no! :P

[Skid]

Correct, its a conditional "no", at least that was Toms Hardwards summation on this issue.

http://www.tomshardware.co.uk/pcie-geforce-gtx-480-x16-x8-x4,review-31964.html

Conclusion
07:10 - Monday 9 August 2010 by Thomas Soderstrom

The big question today was whether or not we needed more than 16 lanes to feed multiple high-end graphics card in SLI, and the answer is a solid “perhaps not.”

OK, let’s call it a conditional "no.”

While we did see a fairly large difference between x8 and x16 slots when a single card was used, adding a second card shifted our limit to CPU performance. That is to say, for most of today’s tests, a faster CPU would be far more important than dual x16 slots in achieving the ultimate SLI performance.

That answer presents its own set of questions, since our high-flying Core i7 CPU was already pushed to 4.00 GHz. Most builders simply can’t go much higher with a daily-use gaming machine.

Another part of that conditional answer pertains to test resolution. GPU dependence increases with resolution, to the point that two cards eventually become a “bottleneck” far tighter than the CPU. Yet, that level of GPU dependence outweighs even PCIe x8 bottlenecks.

In the end, we simply needed a faster CPU to apply everything we learned about single-card bandwidth to multi-GPU configurations. This finding should come as some comfort to owners of “high-end” P55-based systems who might be considering an SLI upgrade for their GeForce GTX 480 graphics cards. If you have a high-performance processor in that motherboard, and you're overclocking to 4 GHz+, the extra CPU horsepower will have a more profound impact than an upgrade to an X58-based machine. Making X58 truly worthwhile requires an even faster processor and resolutions beyond 2560x1600.

[Paradigm Shifter]

That quote, Skid, makes me think I should try taking my 920 back up to 3.8-4.0GHz to see impact on Surround...