you don't have to change the cpu its just strong enough for any modern card......and for the gpu 750 ti is a downgrade gtx 660 is much stronger than the 750ti so if u really want a performance increase go for gtx 760 or gtx 770.....
The GTX 660 is stronger than the 750 Ti.Stick with your 660.
CPU upgrade is better,but even that is not necessary.
If you want to upgrade your CPU however,then get a i5 4690,an i7 is not needed unless you're doing video editing and recording.
you don't have to change the cpu its just strong enough for any modern card......and for the gpu 750 ti is a downgrade gtx 660 is much stronger than the 750ti so if u really want a performance increase go for gtx 760 or gtx 770.....
I agree with Shneiky. Those 'upgrades' you mentioned are far from being upgrades. Your 660 is faster than the 750ti and your current cpu practically performs almost equally to the current i7 in terms of real world performance (the only difference is hyperthreading).