if you can take care of tanking and healing, its cake to find a 5th dps toon. If you want to stick to 4, I would just go 1 prot pally and 3 ele shammys. 3 chain heals can probably heal through anything. Plus if you PuG a healer (rare, I know) you have one less thing to worry about You also might consider 4 manning some instances, because if you can 4 man, the skill of the PuGger becomes less crucial, and you can boot a bad one if they make it worse.

I run a Dk tank and 4 ele shaman, and felt extremely OP in hellfire ramparts even when my DK was 59, and the shammies were 60. At 60/61 its even easier. Have fun!