We tested Battlefield 3 with all of its DX11 goodness cranked up, including the "Ultra" quality settings with both 4X MSAA and the high-quality version of the post-process FXAA. Our test was conducted in the "Operation Guillotine" level, for 60 seconds starting at the third checkpoint.
The tables turn a bit in BF3. Although the GTX 670 performs pretty well for a single card driving a six-megapixel monitor array at this game's "Ultra" settings, the Radeon HD 7950 is simply a little bit faster. Neither card is all that fast, but neither one has any issues with big latency spikes, either. Subjectively, they're both remarkably playable given their FPS averages in the mid-twenties. I'd probably dial back the quality level on both of 'em in order to ensure really fluid gameplay, though.