According to the Inquirer the 2900XT is better than the 8800GTS 640MB: http://theinquirer.net/default.aspx?article=39580
Also the 2900 is cooler than the 8800s.
They say with better drivers the 2900XT could come close to a stock 8800GTX.
Also the 2900 is cooler than the 8800s.
They say with better drivers the 2900XT could come close to a stock 8800GTX.