I've tried ever variation of voltage/clock I can think of. I think there may also be an issues w/ the CPU1 slot. I disabled CPU0 and tried just Linpack on CPU1, it was unstable. I tried swapping the CPU's and the CPU1 slot was still unstable. I am going to throw in my E5649's from my other rig this morning to see if it helps. However chances are I'll be RMA'ing another board.

EDIT: Anyone know what the turbo multiplier is on an E5645?