It will def. be a decent upgrade from the 9500GT but with your build and that GPU it will be hard to max out most games. You would need a little bit better setup for maxing some of the top games. But i must say it is decent mid-range card. Def. better than the 9500GT
An E4300 isn't too bad--it should overclock over 3.0GHz though--just watch your temps when you first adjust settings. Don't leave voltages on auto, manually set them to defaults until you find that you need to increase one for stability.
It should be fine with the Radeon 6750 though, both will bottleneck sometimes, but it's a decent balance.
Agreed. Overall you'll be fine. I have the 5750 and a 1680x1050. I only play Source games (TF2, L4D2) and at 1050 I can max those games out. You should be able to crank a lot of the details up compared to your 9500GT. You won't be maxing out Crysis 1 with that setup, but its a good upgrade and balanced.