I currently have 4 DK team, the main DK being the tank and other 3 dps. Then i just have my healer buddy heal heroics for me. Anyway, from my experience of an all melee group, heroics are a lot harder(usually due to melee range aoe's that some bosses do). Another thing to note with DKs. due to them having some pretty crazy rotations that you wouldn't think would be much of problem with macro's actually are. For instance my DK are pretty well gear and only able to pull at max 2100 dps, compaired to my shamans who can all pull over 3000 dps. Macro'ing dk rotations basically just oversimplifies it and they lose a bunch of dps.