The best answer to that is..."all the way".
Unfortunately there is no real answer to that question, the answer depends upon far too many unknowns. Your best bet here (IMO) is to look up a few overclocks for the 3570k under a Hyper212, see who's settings you understand and can work with (and isn't super aggressive), use that as a base - it may even be that you are unable to reach that. But that's the way I would work it if not wanting to clock from scratch.
Stability is generally defined as being able to run a stressing program error free for 4-24hr with reasonable temperatures, generally 60C or below