you dont need to OC the card, there would be real world gain in it (going from 25FPS to 28FPS is not a real difference)
The 220GT is not really a gaming card. It is fine for watching videos and using Windows Aero and that is about it.
Definitely OC It, Why Not??, Free - Extra Performance Is Just That.... Free And Extra, Id Say Go Up 100MHz On The Shader And GPU Clocks (Seperately) And Go Up 50MHz On The Memory Clock, You Should Get A Decent Boost.