Well, if you try it without raising it, it'll either boot up fine, or it won't.
With some processors, you should be able to overclock quite a bit before raising it.
I have no experience in this though, but once my computer becomes stable, I'll definietly be experimenting
I may not overclock the graphics card though, since doing that on my last board has messed up the graphic pipes.
I think I went a bit too far too fast though. Its something to remember when overclocking. To go slow, so that way if instability occurs, you know where abouts it went.