I ended that run with 51 withered (nothing alive in the instance). Once you've got 30+ berserk withered, nothing really feels theeatening. I still stayed protection (paladin) and pulled judiciously, but honestly I think a simultaneous pull with a boss and a couple big trash mobs would barely scathe them as long as you watched the orientation of the boss (many have cleaves) and your positioning of the ground effects (some cast AOE on you). I've heard berserkers can actually make it harder because they taunt. I just got them yesterday and haven't seen them in action yet so I can't confirm.