What brand psu are you running?
At any rate your buget allows for a 560ti, 69502gb, or in some cases the 448 core 560ti.
If you are gaming at 1920x1080 or below then the 2gb isnt necessary on the 6950 and.my recommendation would then move to.the 560ti or the 448 core if.you can.find.it within your budget.
The 560ti can overclock to.near stock 570 performance while the 448 core comes near 570 performance out of the box and.can be.overclocked even further.
Recap, 560ti 448 core if You can find it within your budget and if not i would say the reg 560ti is the way to go with a single monitor 1920x1080 or lower.
gtx 560ti 448 core is an good card of its price and the hd 7850 or hd 7870 will come out at that time there price will be at high point so it would be better to buy now the gtx 560ti 448 core is nearly comparable towards the gtx 570 which is an good card and after overclocking it performs as gtx 570 so it woulbe an good idea to get now the gtx 560ti 448 core.