Be careful with I5 family processors you choose.
If you go to I5-750 or I5-760, you'll have 4 real CPU cores and 0 threads. All the others only have 2 real cores but have 4 threads.
The first one are true quad processors, the others are basically Duo processors.
The duo processors have usually higher clock speed, but in term of modern gameplay can suffer from having only 2 cores.
In case of OFF, probably the processors with higher clock will be better. But with the possibility of overclocking and thus pushing the clock speed, the I5-750, I5-760 and all the I7 are a much, much better option.
Personally I have a I5-750 2.66Ghz overclocked 3.2Ghz. I could go easily to the 3.6Ghz, but to be honest, so far I don't need. Every game is running fine.