Chest is pretty nice. Things I noticed.
-It can crit
-Damage done is increased by Razorice
-Not sure if damage done is increased by the 10% frost damage when pillar is up, but each stack that is added when pillar is up adds additional damage per stack.
-The effect stays on you when you take off the chest. As in, you could put this on prepull and use it as an assured ~2m damage on pull.
-The effect does indeed work for Unholy