CTRA prevents overhealing.Personally I'm not much of a fan of +healing in raids. It's definitely awesome for 5-man (both for healing faster and saving mana). But with multiple healers in big raids? the bigger your heals are, the more you're going to overheal.
We usually have 5 Druids, 5 Priests and 5 Shamans with us, so no lack of healers. Like I said, i sometimes receive a bit of healing and im usually quite glad then, but i can't rely on it. Anyway, just use bandages and healthstones and you'll be fine, since you shouldn't get aggro anyway. Often you can avoid being hit by an AoE of a boss or if you do get hit, just deal with it.
Greetz,
Death
PS: from my own experience: Maggie fights last quite long, since he got some insane amount of HP. Luci and Gehennas (they're quite similar to fight) don't last so long but still a couple of minutes (you have to take the adds down as well). At Garr I know for sure that the fight is lasting around 10 mins, since i'm on banishing duty there and I cast CoS on the mob which lasts 5 mins. And I have to recast it during the fight. Shazzrah is a very fast fight. After like 3 mins either he is dead or you. Geddon is the funniest fight so far ("You are the Bomb!" Whee!), can't really say how long this one takes. Dunno about the other bosses yet, but since 4 bosses are down now, i think we might get a try or two on Golemagg on Monday (never even saw him so far). /cheer
Edit: BTW: W00t, we got our second legendary drop on Thursday (I wasn't there though). One of the rogues got now both halves http://thottbot.com/?i=37684]Bindings of the Windseeker