Team Fortess 2
For TF2, I cranked up all of the game's quality options, set anisotropic filtering to 16X, and used 4X multisampled antialiasing at 2560x1600 resolution. I then hopped onto a server with 24 players duking it out on the "ctf_2fort" map. I recorded a demo of me playing as a soldier, somewhat unsuccessfully, and then used the Source engine's timedemo function to play the demo back and report performance.

The 8800 GT leads all contenders in TF2. Even at 2560x1600 with 4X AA and 16X aniso, TF2 is perfectly playable with this card, although that didn't help my poor soldier guy much.

BioShock
We tested this game with FRAPS, just like we did the UT3 demo. BioShock's default settings in DirectX 10 are already very high quality, so we didn't tinker with them much. We just set the display res to 2560x1600 and went to town. In this case, I was trying to take down a Big Daddy, another generally unsuccessful effort.

A low of 23 FPS for the 8800 GT puts it right on the edge of smooth playability. The 8800 GT pretty much outclasses the Radeon HD 2900 XT here, amazingly enough. The 2900 XT couldn't quite muster a playable frame rate at these settings, which my seat-of-the-pants impression confirmed during testing.