Best, period is the ASUS Rampage IV Extreme, and I have the Sabertooth X79...whatever you do end up with just make sure it's an ASUS X79. All of the other manufacturers have had so many problems with their X79 MOBO's that at least for now ASUS or bust!
Here's what OC'ers are using -
http://www.overclock.net/t/1167939/sandy-bridge-e-overclock-leaderboard-owners-club
BTW - IMO when OC'ing don't go above 1.40v~1.45v vCore my preference is 1.4v and NEVER a vCore >1.50v or VTT/VCCSA >1.25v BOTH voltages do, guaranteed, ruin the SB-E CPU and I've seen a permanent loss (degraded) of 2~3+ bins from others in a matter of hours; e.g. 5.5GHz -> 5.1GHz for good.
My preference is a 1.4v vCore (or less), moderate to low LLC, and matching...