For gaming, the graphics card is the most important component.
Buy the strongest single card you feel comfortable paying for.
My rule of thumb is to budget twice the cost of your cpu for the graphics card.
If your cpu is a 3570K, then a GTX670/GTX680 or 7950/7970 class card is appropriate.
If your budget calls for a i3-3220, then a GTX660 or 7850 class card is appropriate.
If your budget is for a G860, then a GTX650 or 7750 would be appropriate.
For the most part, graphics cards in the same price bracket will perform about the same.
Yes, there may be differences from game to game, but it is hard to detect the difference without a synthetic benchmark.
Ignore the specs, they are all factored into the general performance equation.
For one ranking of good cards for the money, you can look at the latest Tom's article:
http://www.tomshardware.com/reviews/gaming-graphics-card-review,3107.html
Past that, I would favor the newer 28nm based cards(GTX6xx and amd 7XXX).
They run cooler with less power required.
If you favor amd or nvidia, go that way. They both perform about the same.
I happen to like the nvidi drivers better, and have recently begun to wonder about the nvidia's better consistency of response times.
Read this article on comparing a GTX660ti and a 7950 and see what you think.
I suspect it may apply across the lines:
http://techreport.com/review/23981/radeon-hd-7950-vs-geforce-gtx-660-ti-revisited