I run 1.5V+ core day in and day out on my 890FX, never had any type of problems. I've had my 1090t up to 4.4GHz with RAM clocks pushing 1900, still no problems.
The problem is the heat sink doesn't contact the VRM's correctly. I put a thermometer probe on each VRM, and only the 2 furthest away from the NB stayed below 50*C, the other 3 were in the 60's and the board shut down. I removed the crappy rubber thermal pad, and replaced it with some thicker ones.. I also remove the contact plate on the heat sink, lapped the plate top and bottom and lapped the heatpipe+heatsink. Then I glued the heatsick back on with some Arctic Silver thermal adhesive. That got all 5 VRMs below the 50*C mark.