Supermicro H8QGi or H8QGL series with the highly unofficial and warranty-voiding [H] BIOS will do the trick with overclocking Opteron 6100s. Overclocking is only by raising the HT ref clock; there is no voltage adjustment possible and memory adjustments are very, very limited. If you choose to do this, the H8QGL is the better board as the VRMs are stronger than in the H8QGi. These boards are not originally designed to overclock CPUs and the H8QGi VRMs in particular are only designed to be adequate at stock-clocked SE CPU amperage draws. The VRMs in the H8QGLs are a little stouter but I still wouldn't personally want to risk frying a $700 board just to gain a few hundred MHz.
FYI: I have an H8QGL-iF and have *not* installed the [H] BIOS. I undervolted my Opteron 6234 with TurionPowerControl and as a result it makes much better use of the Turbo CORE states than before. You get a few hundred extra "free" MHz but without drawing more power than the VRMs were designed for, due to the undervolting. This is the ONLY method of tweaking with the CPUs that I would recommend on this hardware.