PCIe Scaling: Crysis
Experience tells us that Crysis is usually GPU-limited, and it appears that bandwidth limits are far less of a problem as resolution is increased.
The x4 slot suffers a 9% performance handicap at 1680x1050, while the x8 slot allows the GPU to reach 98% of its performance potential. That is to say, the mid-sized slot looks like an acceptable option for Crysis.