F.E.A.R.
We're using F.E.A.R.'s built-in "test settings" benchmark for a quick, repeatable comparison.

F.E.A.R. is a lot to handle at 2560x1600, and the GeForce 8800 GTX in SLI handles it best, followed by the quad SLI system. If you were running a GeForce 8800 GTS SLI setup, you'd probably want to drop back to 2X AA or to a lower resolution or lower quality setting in this game.

CrossFire configs have long had trouble with F.E.AR., and the problems continue here. The Radeon X1950 XTX CrossFire system turns in a decent average frame rate, but its minimum frame rate is quite low—and exactly the same, at 14 FPS, as a single Radeon X1950 XTX.