I kid you not, that is how much PCI-E 2.0 running at 16x/8x/8x/8x versus PCI-E 3.0 bottlenecks BF3 and Heaven 2.5 at these resolutions. I attribute this to the massive bandwidth being transferred over the PCI-E bus. We are talking 4-way SLI at up to 10-megapixels in alternate frame rendering. Entire frames at high FPS are being swapped and PCI-E 2.0 falls on it's face.
The interesting part was that while running PCI-E 2.0, the GPU utilization dropped way down as would be typically seen if you are "CPU" limited. In this instance I am not CPU limited, nor GPU limited. We are really at a point now that you can be PCI-E limited unless you go PCI-E 3.0 8x (16x PCI-E 2.0) or faster on
all GPU's in the system. GPU utilization dropped down into the ~50% range due to PCI-E 2.0 choking them to death. As soon as I enabled PCI-E 3.0, the GPU utilization skyrocketed to 95+% on all cores. I was going to run more benchmarks and games but the results are such blow-outs it seems pretty pointless to do any more. It may interest some of those out there running these new PCI-E 3.0 GPU's in which they think they are CPU limited (below 95% GPU utilization) yet might have PCI-E bandwidth issues.
Down to the nitty gritty; if you run a single GPU, yes; a single
16x speed PCI-E 2.0 slot will be fine. When you start to run multiple GPU's and/or run these new cards at 8x speed, especially in Surround/Eyefinity, make sure to get PCI-E 3.0.

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