The Vcore may alter automatically if the SerialVID works perfectly, basically the board automatically adjusts the Vcore to suit.
You just set the multiplier from 33X to say 40X, then re-enter the BIOS, then have a look at the Vcore, if its increased on its own while still on AUTO setting then your good to go.
It should change to this,
Stock-4GHz on Stock VID
4.0-4.3GHz 1.300v-1.325v
4.3-4.5GHz 1.325v-1.375v
4.5-4.8GHz 1.375v-1.450v