I get very reasonable framerates @1024 x 768 with the specs in my sigiture and the settings cranked up reasonably and high aa.
I still get reasonable framerates @ 1280x1024 but I have to turn down AA to 2x and disable most of the special efects. Shadows were off I think.
With only twelve pipes I doubt my x800gto is going to be a star peformer, no matter how much overclocked. An XL should be better.
Still not keen on the game itself though. It's all a bit....humdrum so far in my opinion.