Finally. One of those things that did not belong in a well designed videogame.
You will be able to reach 50 stacks, idk if it will be optimal. As buffing the mastery increases both the mana pool and mana regen, you will have good chance to do it well before a 2nd evocation
It seems like nether tempest's arcane missiles proc rate was greatly reduced.
I cast 50 nether tempests on the dummy and got 1 proc.