You have to give us the specs of your PSU. If it is very low power, you might not be able to run anything more hungry than a GT630... But globaly, 750ti is a good idea even if your CPU will certainly bottleneck. Maybe it would be cheaper and not so much less powerfull (because of said bottleneck) to take a 7750.
At any rate, I would probably take a graphics card without dedicated power supply.