680 has 640 more cores than even 2x560Ti-448 cards. I'd be tempted to hold out for a 680 as it runs cooler than 2x560Ti's and is a single card. Read the review here in Tom's. 650W PSU will run a pair of 560Ti-448's fine.
jjack...Kepler 680 IS launched and reviewed here in Tom's. As for CFX, Radeon cards are crossfired, Nvidia cards are SLI'ed. How do you figure 2nd card is barely used? I run 2 cards in SLI and according to my Afterburner charts both GPU's are used at the same rate.