If it's the 1gb 5870 then I understand your limitations. I'd say only if you are hitting a vram bottleneck and must have nvidia and can't afford more than a 660, then it would be worthwhile to get a 660. Otherwise, like dheeraj said above, the 7870 is a great card. If you want nvidia then I'd look for a 660ti or preferably a 670 to make it more worthwhile.