Well, tbh, when you look at all the specs, while you increased your mem clock and speed and doubled your cores, the overall bandwidth speed is only slightly better and same with your fill rates. GPUs are the hardest thing to upgrade due to the small changes made beyond memory speed. So most folks will see mem speed and go "Holy SH!T that's awesome!" Only to realize that MAJOR parts that matter are marginal at best with changes. If you had a crappy 9600GT like mine and went to the 260 or the 560, you would notice the difference. Other thing is, some games go about the use of your GPU differently then others which maybe why you see significant changes on games like Witcher and such.

Honestly though, keep the card it's not going to hurt.