is this voltage ok for my overclock?

hey everyone, i dont quite understand the voltage thing but here's what ive done so far. i used nvidia control panel to overclock my cpu from stock 2.5GHz (Q9300 with multiplier of 7.5x) to 2.7GHz. and its running at 2.7GHz because thats what cpu-z says. i trust that cpu-z doesnt lie. it mustn't because 3dmark vantage rates my internal cpu clock at 2.7GHz also. but my question is a voltage of 1.238 good for this overclock? my pc is running fine, a little faster. is there any way to test the stability of this overclock? i guess that the voltage only needs to be changed after i oc and my pc freezes right? then i would up the voltage. if that sounds right or wrong please let me know as to im very happy i overclocked for the first time and nothing went wrong. thanks to all who help in advanced

ok thanks, i guess i cant use the pc while those 2 hrs are going. and also i only raise the voltage after i freeze the pc right? because i would like to get a higher clock speed. maybe 2.8GHz-3.0GHz. but unsure as how to treat the voltage. go as high as i can with current voltage, take note of fsb when i freeze the pc, then reboot and raise the voltage to next setting and continue from freeze point? does that seem right as how to overclock the cpu? thanks for any help in advanced.

ok thanks again. ill check it out