I recently RMA'D my 560 ti and got it replaced by Cyberpower. It turns out when I got my package back today they had sent me a 660 in return. Did they just send me a better card?
I do agree the GTX660 is the stronger of the two cards. Not that a 560Ti is a bad card. And yes they gave you the better card You are lucky there sir keep your head low and mouth shut
The GTX 660 is about 35% better than the GTX 560Ti - and you get double the VRAM.
They probably don't make any GTX 560Ti cards anymore and sent you the closest card they currently produce. Just be glad they didn't try to foist a GTX 650Ti on you...