thanks for the answer. i was thinking 4.0ish might be pushing it. so other editors pushing to 4.5 and not getting lockups/crashes?
The 3930k is really easy to overclock since it is an "unlocked" cpu.
So, maybe start with around 4.0 / 4.2 GHz and see where your temperatures are after a long render that is taxing all cores. Then bump up your speed to as high as you can but without exceeding 70 deg. C or so.
What are you editing 4k? Your CPU is likely more than fast enough already and the least of your worries--it not like gaming where speed is paramount. In fact, due to increased stabiltiy errors, its likely to get worse.