Surely someone can tell me whether it is possible to overclock on any of these motherboards?
I'm sure you've already resolved this, but apparently H55 boards can't be overclocked. At all. Just called Scan to ask about potentially unlocking mine, they said it can't be done but they'll refund me for the board...
A P55 should be fine though, just remember it'll mean you can't use the integrated graphics. Not that you'd want to, I'm sure.