1dk tank + 3 melee dps + druid healer, works perfectly fine in 5man heroics. I have no idea how it compares to tank + 3 casters + healer though as i've never played that type of team makeup. I would assume that they will find some bosses easy which are more challenging for a full melee team and vice versa. Anything with 1 tank and a healer will be fine, but My only advice is that you go full melee + mobile healer (priest/druid), do not mix and max with say 2+ melee + people with castbars as that would just yuk to play IMO