I wouldn't start messing with voltages until you've seen how much extra you can get at stock. Play with the clock speed and/or multiplier until you have something stable then leave it like that for a while, keeping an eye on temperatures. If everything is good after a week or two of normal use, increase the voltage slightly and repeat. The key to getting good at OC is to take things slowly, always monitor temperatures, and always increase settings by small steps, testing for stability each time.