If it's a Wilamette core, I doubt you'll hit 2.2GHz even with voltage bumps, as the Wilamette core didn't see past 2GHz. With a Northwood core, you could look at upto 3GHz with some modest voltage bumps.
If you don't know what core you have, you can download [google]CPU-z[/google] and it'll tell you what core you have.
I know you're nervous about voltage, but as long as you stay below 1.65V, you'll be fine. However, it's always best to start with the stock voltage, and see where that gets you. I'd also recommend running [google]Prime 95[/google] for 24 hours to make sure no errors are popping up.