As long as you're staying under the max AMD specified safe voltage and temperature (mainly temperature) then you'll be perfectly safe to nudge the CPU voltage up a tad.
If you're wanting to keep it at stock keep notching up that CPU multiplier until you aren't stable.
Remember, reboots, bluescreens, and lack of stability won't hurt your motherboard. (restarts can hurt your hard drive a tad if you are using it during the restart, assuming you aren't using a SSD)
I usually run the Prime95 for about 15 minutes while I'm adjusting settings. Then I'll run it for a few hours once I get a setting I'm happy with to be sure I'm completely stable.
Yes some people run it for 24 hours, however I haven't ran into stability issues after using my 3 hour (or so) rule.