With voltage too low, it will lock up or crash, hence increasing voltage to oc. As for too high, it would cause higher temps and shorten life. Unless you WAY increase voltage (like past what mobo allows) I dont think it should be a problem. As for default...I think its around 1.6 or so, I know I run my 800 @946 at 1.7 volts or so, no probs. If I oc anymore I have to run at 1.75 (The max my board goes) and I'm not comfortable doing that since I dont have the money right now to replace something if I fry it, so I try to be conservative (800 @ 945 @ 1.7 volts...Is that conservative?)