GTX750TI or GTX660 for GPU rendering


I would like to buy a GTX750TI or GTX660 vga card but I don’t know how much the difference between the two on gpu rendering. Could someone help me in this?
I saw the 2.6 cycles render benchmark thread but I saw quite different results with the same card so I could’t make any conclusion…
Theoretically the GTX660 is better but more expensive too so my question is how much better?

Thanks in advance!