I've been tanking the infernals myself with about 200 FR before Aura and I was getting nothing, but 75% resists last tuesday in Hyjal. I'd wear more FR, but I need the threat to allow ranged to kill the Infernal before the next one spawns. We usually only have 3 tanks, (MT, myself, and either our Feral tank, or one of our Fury Warriors) so that forces me to tank the Infernals solo, but if I had a choice, I'd probably let a Warrior do that and put my healing gear on; my lolhealing would probably be a bit better than a Warrior's loldevastate spam.
We use 6-7 healers for learning fights and I didn't notice anyone OOM, or uncomfortable while healing that particular fight.
Our advantage is that we'll obtain a bit higher TPS on the Infernals than a Warrior will, and our threat will come more front-loaded from Judgment/Exorcism/Avenger's Shield at the start. Depending on your strat, we're also more of a safety net for catching the Infernals. You'll probably have that one person in your raid that won't run to the center of the road, or your Hunter will miss a spawn. It's nice to know you can reel it in yourself.

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