Just the hyper threading on the i7's will artificially show lower cpu usage on any game that can not use all the threads as well.
If you play MMO's just note that those will jump from CPU to GPU demanding as well. My 2600K @ 4.4 is not enough for large scale guild wars 2 battles. It is playable, but has NO CHANCE to hold 60fps in these large scale events.
I played Bioshock Infinite with the default settings without any issues on a 650 ti(with the same cpu above when my 670 was in RMA), you should at least get med settings on a good number of games and high on less demanding games.
Please note that frame rates will vary to an extent on almost any system.
You can get an idea of average performance under different games here. Please note the settings are higher than recommended for optimal performance on more demanding games.
http://www.techpowerup.com/reviews/NVIDIA/GeForce_GTX_750_Ti/7.html