I'm assuming you're running with 4x Totem of Wrath, so your +hit is pretty good. 12%
You need 16% spell hit to reach the cap on level 73 mobs as 70.

/edit 17% hit? The hit rate on a +3 mob is 83% and you will always have 1% chance to get resisted. Meaning anything above 16% should be a waste.

Edited to remove wrong information