What CPU for GTX 660 TI (LGA 775)

Hi,

Well the fastest LGA775 cpu is the QX9650, and would run on your system. However, even that CPU will hold back the 660ti somewhat.
the 775 socket is long dead, and so upgrading has only limited options.

I'm in the same boat myself, with a q6600 @ 3ghz, and I really need more juice now, as games are becoming so demanding.

Time for me to upgrade the system soon, and will be for you too  

I wouldn't recommend upgrading to the old tech, perhaps save your money, and get a few bits to make a new system, thereby complimenting your 660ti and having a more balanced system.