The 750ti is a nice card because it's very low wattage even at peak.
As for gaming, the 750ti is close to a gtx660:
BF4 around 50FPS on high settings 1900x1080http://www.bit-tech.net/hardware/graphics/2013/11/27/battlefield-4-performance-analysis/3
Arma 3 53 FPS on 1900x1080http://www.tomshardware.com/reviews/geforce-gtx-750-ti-review,3750-7.html
Watchdogs 34 fps on ultra 1900x1080http://www.tomshardware.com/reviews/watch-dogs-pc-performance,3833-6.html
But, because you are limited by your CPU, you may experience 10-15fps less than the average amount. Lowering the settings or resolution can remedy this though.
As a side note, the 750ti can be used in many prebuilt computers or old computers because of the low watt requirement even if the PSU are bad.(it varies, but in general)
So make sure to give it some use elsewhere when you get a new GPU.