The Elder Scrolls IV: Oblivion
We turned up all of Oblivion's graphical settings to their highest quality levels for this test. The screen resolution was set to 1280x1024 resolution, with HDR lighting enabled. 16X anisotropic filtering was forced on via the cards' driver control panels.

We strolled around the outside of the Leyawin city wall, as show in the picture below, and recorded frame rates with FRAPS. This area has loads of vegetation, some reflective water, and some long view distances.

When is getting the best frame rate not a win? When the card doesn't run the game very well. FRAPS didn't seem to catch it, but all of the Nvidia cards we tested had performance issues in Oblivion. The game would hesitate momentarily as we walked through the vegetation, seemingly at each point where there was a level-of-detail change. This game uses an awful lot of dynamic LOD scaling, so that means lots of quick pauses and hiccups. The GeForce 8600s have the shader performance to suffer from this issue and still produce good frame rate numbers, probably due in part to their ability to dedicate lots of computing power to vertex processing in this crazy-detailed area.

We have seen GeForce 7600 GT and 7900 GS cards run Oblivion quite smoothly in the past, so I expect this is some sort of problem with Nvidia's Vista x64 driver.

Rainbow Six: Vegas
This game is notable because it's the first game we've tested based on Unreal Engine 3. As with Oblivion, we tested with FRAPS. This time, I played through a 90-second portion of the "Dante's" map in the game's Terrorist Hunt mode, with all of the game's quality options cranked.

I'm starting to think the real loser here is the GeForce 7900 GS, which gets humiliated by the GeForce 8600 GT once more. For its part, the GeForce 8600 GTS can't quite catch the Radeon X1950 Pro, but it's very close once again.