I know this emulator, is relies heavily on processor speed (it has to emulate 3 different CPUs, all of different types/architectures.)
I have a Celeron Dual Core E1200 overclocked from 1.6 to 3.0 GHz on an MSI P35-Neo motherboard, which is in the same family as the G31, yours. I also have a G31 in another computer and it overclocks just the same, just make sure you buy or have a better cooler, the stock won't be enough for 3.0 GHz.
I have an ASUS Triton 77, which gets me around 45°C idle.
I would increase by 25 MHz everytime, pay CLOSE attention to the temps, run PCSX2, push it to the max until you know it's safe (or use pressure test programs) and then increase again.
3.0 it not that much, you could go for 3.2 GHz on that, with a little vcore increase, but maybe not even.
The G31s are bad overclockers overall, but for you and me, FSB is all we need to change. Like I said, watch your temperatures!
50°C is too hot when not doing anything (idle), you want at least 47°C. 52-55 is pretty good on load.
Chris
EDIT: By the way, go into PCSX2's CPU configuration and enable MTGS (multi-threaded GS mode), I can garantee you a 60% speed increase. Also, download the latest PCSX2 beta and plugins, also a major speedup. (If you really want speed, in the new PCSX2, the speedhacks, under config really speed up the game.) I play Kingdom Hearts Final Mix + @ 60 FPS with this.