Really the only time the R420 based cards performed differently than their R420 counterparts was when Anti-Aliasing and Anisotropic Filtering were enabled and we were running the game at high resolutions. The ATI Radeon X800 XT Platinum Edition was able to run around 7 FPS faster at 1600x1200x32 with 4X AA and 8X AA enabled, compared to the approximate 1 FPS difference between the two cards at every other setting.

This is a good indication that ATI probably has a winner on its hands with games based on the Source Engine, but really it's a little too early to tell. Also, Counter-Strike: Source does not seem to be as graphically demanding as some scenes in Half Life 2 that we have seen, so we might be able to see some variation in performance when the game finally ships sometimes in August.