+4 really, as you get an extra +2 Charisma from Angelic Presence.
I use exalted angle on mine as well with a necro twist in from magister,
150 fire/+6 necro thunderforged in one hand,
100 potency/+7 spell penetration thunderforged in the other hand.
I'm too lazy for tier 3 thunderforged... but if i did ... +22 fire crit.