I 3 box: Prot Pally, BM Hunter and Elemental Shaman. They're all 78 atm.

Yesterday, I cleared normal Drak'Tharon Keep with just the three of them. I have no idea if I will be able to do Heroics but I'm going to try. 95% of trash is no problem, but some bosses in normal have been a road block. I either don't have enough DPS or healing.

However, I think there is huge potential there. My shaman, even geared and spec'ed for elemental, can still heal really really well. In fact, he'll DPS most of a fight and throw an occasional heal onto the tank or a chain heal to the group. When I hit 80, I'll spec the shaman full resto.

Honestly though, I think the bigger issue isn't the group, but my over all ability to handle an encounter (ie. the mechanics) and that's going to be a problem 3 or 5 boxing. You just have less room for error with 3 boxing.