For 5 man, i suggest to remove the priest, all 5 other work in perfect synergy for caster buff, priest got the spirit and endu buff.., you can also remove mage from this comp if you prefer but priest got channeled spell who broke follow and turn the char, facing another direction than other toon. This is annoying for starting Mbox
Prot pala - DemonoLock - ArcaneMage - Boom - RSham
The boomi can get a second spec tank if you want second tank for doing achievement or something else, sham must have a second spec elem, cause when you are geared, you will not need healer spec for heroic dungeon
This team is my base-group for caster, then i adding 5 spriest (or 5 other..) to get a decent raid comp. If you want to extend to 10box later