Yep, the 6800GT is the best there.
They go in terms of this with Nvidia:
Vanilla (Standard) like 6800, GT, and then Ultra.
All would produce good settings, and if you have SLI, I'd get 1 6800GT if you can't afford two as yet, and then wheny you can afford it, get another one.
I wouldn't get a 6600GT if you can afford a 6800GT for example, only to want a 6800GT later on, as 2 6600GT's would probably equal (not exactly sure) 1 6800GT.
I hope this helps