PCIe Scaling Summary
Today’s benchmarks include a wide variety of data on different games and resolutions, making it hard to keep track of the score. We're bundling those titles to give you a better idea of the general performance profile for the most common enthusiast-level monitor resolutions.
Enthusiasts on lower budgets will find a general performance loss of 2% to 4% when switching from an x16 to an x8 slot. That's not altogether bad. Some of that difference will accumulate in SLI and CrossFire configurations, and we will address that topic in a later article.
PCIe x4 slots hurt performance by an even greater amount, and the loss is most significant when using an AMD graphics card. The real shame is that, even though the performance drop is less dramatic for GeForce graphics, the x4 slots of P55 and P67 motherboards don’t support SLI due to an artificial cap imposed by Nvidia, presumably to sell more NF200s.
Performance losses shrink marginally at 1920x1080, but one can still expect a 10% to 18% drop when using a x4 slot.
At 2560x1600, the performance loss of an x8 slot drops to 1-3% as the bottleneck shifts to the GPU, rather than the pipeline to which it's connected. The x4 slot is still a poor compromise, losing 7% to 14% compared to what most of us would probably consider the proper configuration.