Play Quake III Arena, Unreal Tournament, Counter Strike etc for few hours. If it doesn't crash then most probably your OC system is stable. I could do 3DMark2000 looping tests but my system crash after about 30-45minutes of Quake at 1GHz and above (v-core ranging from 1.7-1.85).I couldn't even load UT on my machine. I still cannot figure out why?
My system can do almost every Windows application @1035Mhz at 1.8v but no go for games.
Good luck