I'd pull with mindblast instead of mindflay... i would think you would want the aggro on the priest more than the mage.
then i'd hit something like SWP and Frostnova depending on how close the mob is.
if mob is already ontop of you use SWP with Fireblast
and then finish with Mindflay and arcane missles.

Just know that if you are relying heavily on Arcane missles for dps you are going to drink alot. Its a huge mana hog.

If it were me playing this is what i would do.

Mindblast / Frostbolt
SWP / Fireblast
Mindflay / Arcane missles
wand to death if any health is left.