I'm going to upgrade my GPU. What should I get?

coolmarquis97

Honorable
Mar 27, 2012
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Currently My Specs are as follows:

Intel i5-3570k
8gb of Ram
Asrock z77 Extreme 4
750 PSU
GTX 550ti

I'm looking to upgrade my GPU and don't know what to get. I've been looking at the 7950, the GTX 670, the GTX 660ti. Which of of these is the best or is there an even better card?

(Price range is about 300-400)