i love how people are comparing the clocks... and ONLY the clocks of the 6800gs and the 7600gt. sure the 7600gt doesnt lose in benchmarks... but it only wins by 10% and a 1000 vs 1500 is like a 50% increase, this is where 256-bit vs 128-bit comes in.
and about the x1900xtx vs the 7900gtx, they're better for different games. he included the fact the the x1900xtx has 8 less pixel pipelines, but did he include that is had 40 more vertex shaders??? NO HE DIDN'T! this is why they perform similarly, but different depending on wether the game demands more pixel pipelines or if it demands more vertex shaders.
basically when it comes down to it, you need to buy the card depending on the games you play, but the x1900xtx = 7900gtx in performance, varying upon the game. one might has 5fps less in one game, and the other 5fps less in another, but overall they're the best cards you can get.