No direct comparisons between the cards you are refering to. 512MB helps in a few situations like in COD2, but overall has not really shown a significant bonus over 256MB cards.
The 256MB X1800XT is easily equal to a 7900GT.
This review tests a 256MB X1800XT vs a 7900GT and the X1800XT handles the high resolution AA/AF settings better, which to me shows it's the more powerful card. Just glancing at the charts the 7900GT could look like the better card, but focus on 1280x1024 and 1600x1200 with AA/AF and it's almost a clean sweep for the X1800XT. And afterall who buys this caliber card and doesn't try to crank the eye candy. Of course it all depends on the games you play so either card potentially can be superior to the other depending on the individual.
Actually I have never heard of Colorful, but I hope the cards' performance as well as their tech support is faster than that website of theirs 8O :tongue: . The card seems factory clocked so I doubt just the 512MB mem is going to do much extra for it. My only issue with the 7900GT besides being worse in Oblivion, is
the issues that many factory OC'ed ones are having. I'd have no problem buying one but it would be from a well known company like eVGA or BFG. If Colorful is know for outstanding customer support and warranty service :?: , then it's a fine choice. If not, I'd stay away. Anyway, just my $0.02.