I would suggest going with a 660 over a 560 ti because you will get a performance increase over the 560 ti AND the 570 for the same price. Not to mention if you are running a PCIe 2.0X16 slot with your current motherboard the 660 is backwards compatible and will run in that motherboard, and you will not see a difference in performance even though it is a PCIe 3.0X16 card.
Also... I hate laning against mordekaiser -_-
Haha who doesn't if your looking at my OC specs I'm upgrading everything