I have to agree, I've got 2 Computers both with similar specs, one has the X800XL and the other has the 6800-GS. Gaming wise the X800XL on BF2, Quake 4 & FEAR can run at full detail without a problem. The 6800-GS however runs BF2 on medium and struggles on high, but runs Quake 4 and FEAR ok (slighty lower fps) on high detail.
So, my personal testing shows the X800XL just in front.
BullDog(UK)