I meant Low - Medium - High or Ultra on a 6800GT
I can run Ultra fine @ 1024x768 on my GF6800 GT (would try higher but this 15" monitor wont handle anything above 1280x1024), only issue I come across is the sligt pauses between rooms due to the game caching all the geometry/textures through the GPU.
Anyhow, I'd go with the 7800, it should be faster with things like HDR & PS3.0 no? And as the others mentioned, can always SLI it up at a later stage.