6800 GT or NU. It is hard to recommend the X800Pro at that price range as it constantly gets beaten by the 6800GT. And you already said that the X800XT and 6800U(E) are out of your price range. So i would say 6800GT first, then in a distant second the X800Pro. THe 6800NU isn't hard to recommend because it is a good price performance ratio, however if you have the money go for the GT, if you absolutely dont want a GT then the X800Pro, but GT first.
-Kevin