Well if you have the money, and by January, both will not offer any games, so the 660ti(about the performance as the 7950, a little cheaper) is better choice by then or the 670 gtx(which is much better than the 7950, but costs also more).
It all depend on the price variations.
Also like i said since you have a 560 gtx, you could wait a bit more for the amd 8xxx series or nvidia new gpus and the new intel cpus(haswell) for 2013.
Or else if you don't wanna wait, buy the i5+z77 and the new card, and sell your older card afterwards.