What the HELL - x16/x16 vs. x8/x8 crossfire

http://www.tomshardware.com/reviews/crossfire-pci-express,2095.html

I don't have any revelations about this. What I can tell you is there is about a 5% performance loss with x8/x8. However there is a rule of thumb that might work.

As you increase the graphics processing requirements such as higher resolutions usually above 1600 x 1200 or as you turn up the shader and AA as your FPS drops the gap between x8 and x16 will grow larger. Now understand this is with both cards running at x8 or both at x16. A single card of the same model will never out pace a crossfire setup.

If your above 60fps on x16 you won't see much change. You might see 58fps on x8

At 50fps you will see about 45fps on x8. At 40fps you will see about 25fps at x8.

So this basically tells us the harder the cards work the bigger the gap. If you aren't pushing the limits of the cards you will likely only see your best performance gains with crossfire at very high resolutions.