Doom 3 - High Res
Doom 3 (and all games based on the engine) will surely benefit from Quad SLI, as it keeps the anti-aliasing enabled line close to the AA off line. This keeps with findings we saw in the 3DMark tests.
Half-Life 2: Lost Coast - High Res
Interestingly, it's a different story when it comes to Half-life 2: Lost Coast a different story. The low resolutions do well in a head-to-head comparison with the features turned on and off, which indicates that the game is CPU limited. As the resolutions increase the non-featured line stays almost horizontal, while the feature-enabled line starts to fall. At 2560x1600 the Quad system can still do almost 58 fps. That is excellent considering how much rendering it has to do - over 245 Mpixels a second!