Overclocking is very much trial and error. You increase the speed by small margins and then test to see if your system is stable. If it remains stable, then you can increase it again by a small margin and retest. You continue this process, incrementing by small margins, until your system fails a load bearing test; at which point, you down-clock to the last stable point you previously tested.
I found
this article which may help you.
-Wolf sends