You can save Mirror Image, Frozen Orb, and Icy Veins running Thermal Void and Frost Bomb for the transition and there is no way Arcane can touch that damage. You also have to consider that you wouldn't run Rune of Power on Imperator and Arcane isn't that much higher than frost right now.
Frost has way more globals to use while moving, using Arcane Barrage any time you have to move messes with your dps a lot. You also don't ever have to worry about Rune of Power as Frost.