From what I gather, the performance gain for games is somewhere around 5% at best. Question to you is of course if that's enough for you to deal with a 20% increase in price. It also depends on what you're spending on the rest of your system. That $20 extra may not be much if you're going for a top of the bill graphics card. In any case, have a look at
http://www.phoronix.com/scan.php?page=a ... =219&num=1 to get a better perspective of the differences between the two chips.