Unless the 256mb vmem severely cripples the performance of the x1800xt, it should spank the 7900gt in most cases, as well as offer newer features and better IQ, seeing how the 512mb xt was overall faster than the 7800gtx. For the same price, it's a no brainer. And the 7900gt cooler is loud, so it doesnt have the quiet thing going for it like the gtx.