Despair
PvP 1x Damage
PvM 1.5x Damage
PvM with Slayer 3x Damage (Or 2x the 1.5 for PvM)
Tribulation is the same damage PvP/PvM
Tribulation with slayer is 1.5x Damage.
Switching masteries doesn't fit into the big "master" plan which is about as much as I can say about that.