Far Cry 2
We tested Far Cry 2 using the game's built-in benchmarking tool, which allowed us to test the different cards at multiple resolutions in a precisely repeatable manner. We used the benchmark tool's "Very high" quality presets with the DirectX 10 renderer and 4X multisampled antialiasing.
Our two main contenders are very closely matched here. The Radeon HD 4850 1GB is faster at mere mortal resolutions, but the GTS 250 produces higher frame rates at four megapixels.
The most notable result here, perhaps, is the strong performance of these two new 1GB cards at 2560x1600, where even CrossFire and SLI configurations involving 512MB cards run out of headroom. Neither new card, in a single-GPU config, is really fast enough to be playable at this res, but the additional video RAM clearly brings an improvement, and these results suggest good things for multi-GPU configs with 1GB. (So do our results from higher-end multi-GPU configs involving 1GB cards, of course.)