I've already listed some mainboards for overclocking...
I recommend these boards:
ASRock P67 Extreme4
ASUS P8P67 Pro
Find them on NewEgg yourself -- the Search function is quite good on their site.
Unfortunately, there are no "super overclocker" steppings for Sandy Bridge CPUs. There's no real way to tell how each one will overclock unless you set it up and try it out.