Copper for your thoughts, re: 3-box groups

This won't be happening for some time yet, but after I'm done what I have planned to do I'm going to have six 60ish toons to level to 80, spread across 3 accounts. Trying to figure the best group compositions and specs to level them with for ease of playing, speed, efficiency, etc.

Five of the toons will be freshly boosted/gifted 60's with no gear, gold, mounts, flight paths, rep, NOTHING. So they'll have to be geared initially from cheap AH items. The sixth toon is my DK, who is a couple bubbles shy of 62 and as a DK, well-geared from the starter zone quests. So he'll have to escort the others through quests he's already done initially.

Anyways, I plan to drive with the DK in one group and the warrior in the second group. So here's the six toons I'll have to work with and plan to make two holy trinities, thoughts on who should go where for ease of macroing/etc and efficiency/buffs and such?

* DK
* Warrior (Prot?)
* Mage (Fire?)
* Lock (Demo?)
* Shaman (Resto!)
* Druid (Resto!)

Obviously the "tanks" will be specced for tanking, the hybrids for healing, and the dps'ers need the best, most complementary-to-the-group and mana-efficient dps specs to minimize downtime. Which I'm not sure of...having never previously played a mage or lock above L30...

if your going the holy trinity route (1 tank 1 healer 1 DPs) then Id suggest this.

Unholy DK - 13% magic dmg and a good aoe tank
Frost mage - most aman efcient spec and strong aoe, note you want this with the DK for sure simply becuase the DK wil give a melle slow on the target at all times and with torment the weka thats 12% more dps
resto sham - personaly Id go ele though and off heal as needed unless u plan to 3 man instances

prot Warrior
demo loc - for mana efficency. though afli is more mana efficent imo it just doesnt work well in groups killing too slow.
druid - same as sham here Id go boomkin unless u plan to 3 man instances, just have a nice hot macro then swop to boomkin or just nuke.