To answer this, start at stock. Play for a while. Then, overclock just a little bit and play for a while. Then, overclock some more and play for a while. Keep doing this until you get to like let's say 4.5 GHz. If you don't notice any difference between stock and 4.5 GHz (which is what I'm expecting), then you don't "need" to overclock. On the other hand (of course), if you keep noticing superior performance with each increase to the clock speed, then you do.
So, it depends on you and what you want and like or don't want and dislike in performance. I mean, I feel that this is a question that can only be answered by experimenting. In other words, answering "how high should I overclock for this" (or that, etc.) is really best answered by "you".
Another thing that you can do is this: try stock first and play for a while. Then, go straight to some round number like 4.5 GHz.
There's one catch though: with each increase to the clock above stock, you need to test the stability before playing. If it's not fully stable, then you could get worse performance than stock. In order to see the true benefits for you (if there are any), it must be fully stable at each higher clock.
Edited by TwoCables - 3/15/14 at 8:13am