Take the 660 Ti out of the equation.
The 760 and the 7950 go blow for blow at stock, but if you are going to overclock, the 7950 will have a much better chance of hitting higher clocks. If you are going to overclock, go with the 7950, and if not, or a light overclock, go with the 760. Just make sure you pick a good model of the 7950--certain ones will have a better chance of overclocking higher.