its not really a matter of brand as to which one scores better. but rather the clocks they are set to, and you can set those yourself. honestly both of the brands you mention are very good and you wouldn't go wrong with either. they have good warranty's, evga has a step-up program, and they are both generally accepted as two of the best makers of nvidia products.
check newegg, they usually have some good deals. currently the have a xfx 8800gts g92 for $299 with a $20 mail in rebate. which is a **** of deal if you ask me.