I'd take a 560 Ti 448 core, probably. They overclock ridiculously well. Speaking of which, you have to get a 2500K. OCing it will be easy and safe, and you'll get a whole bunch of extra performance for free.
It depends on you. Can you wait or do you want to jump right in and start playing the games. If you want to do it now, later you can always sell your card and buy the new Nvidia Kepler or AMD 7xxx series on down the road.
Any way here is link to a chart for the 448 core I wish I could afford them myself because I would get two for sure. The second link shows the cost of one and just two days ago it was 289 dollars now it is lower.
We don't know yet if the new cards is going to be good or not, what if you already wait and the performance is disappointing? You'd better get now and with no wait. For $300 you can get the 560 ti 448, because you can get the price to performance for a card. It's also a limited edition so you better get it as fast as possible . Here: