Actuallly 2 7300's SLI sometimes beat one 7600GT, but it all depends on upgradability, price, games you play, what setting, specs of your computer, etc.
dude don't look into it trust me cause i got a crappy geforce 6800 xtreme and upgraded to an evga geforce 7600gt which i should've just bought that card in the first place.
go with the 7600gt. why buy an ati card when you have a sli mobo. just buy the 7600 now and then get one in a month or two. that would be the better choice.