I was in a hc a few days ago, we had a dk tank who just pulled and pulled.. him and the healer were fine but he must have taken a lot of healing as us dps kept almost dying from stray mobs that aggro'd onto us.. he was full mythic geared and was pulling 40k dps.

I also vote healer... but I'm not sure that would be enough.. so maybe a 3rd as a dps.. a hunter maybe for full movement?