What is the make/model of the GTX750ti?
If it does not need 6 pin power, you are likely ok.
Do not expect much.
Overclocking is potentially harmful if you make a mistake.
Before you try, try this test to see if you would benefit:
Run YOUR games, but lower your resolution and eye candy a little bit.
This makes the graphics card loaf a bit.
If your FPS increases, it indicates that your cpu is strong enough to drive a stronger graphics configuration.
If your FPS stays the same, you are likely more cpu limited.