Q9550 (C1 stepping) @ 3.6GHz with 1.31V Vcore here.
Runs under full load with decent temps and completely stable.
This CPU is rated to take 1.36V Vcore so all is good.
I would however suggest you post what all your voltage settings are for the experts to see and also run Prime 95 to check stability for an extended duration. (8-12hrs)