You may have gotten a better GPU for your PC, but I have a feeling that Pentium G620 is going to bottleneck your system. Meaning, the graphics card will be too fast for your CPU, thus creating a "bottleneck." Also, how much do you have in you power supply unit (the box that powers you PC), if you only have 350W power supply, it won't run the GPU at it's fullest capacity.
The GTX 750Ti requires at least a 300W PSU. You're capping out on your power with that. The 750Ti may only draw 60W of power, but it's recommended to have above the required wattage. Without a doubt, you will see better performance, but your new GPU may be severely stunted due to the limitations of your CPU (and possibly your PSU). You can always check if you want. A sticker should be on the side of the box. Just open you PC's side panel.
Well, hope I didn't sound too off putting. Contrary to what Giant Army says about the specs required to run this game, you actually need way above what they recommend as a minimum. That's just the way it is, and that's probably the way it's going to stay. There is just no way you can run this software with a run-of-the-mill desktop or laptop. You can (kinda), but you're experience will be somewhat hindered.