Hey Lud, the issue you'll have with that setup is that it's extremely weak on DPS, everyone has their preferences for how to to play, if this box setup works for you, well crack on, but you'll run into a wall with the higher level content where you will just not have enough DPS.
I run all kinds of different group setups, but what I've learnt is don't run bards unless it's a pure melee group, default to using an enchanter every time, shaman's can take the place of a healer, just never ever take one expecting them to do DPS, because they don't, yes their ADPS they add to a group is awesome, but I find they are lacking (don't get me wrong I love shamans!!!!).
When I used to only run 4 accounts +2 mercs, I would setup like this:
SK or Warrior for main tank/puller
Enchanter for CC and DPS (yup enchanters can do nice DPS endgame)
Cleric for heals, nothing can beat them for sheer heal output
Berserker or Wizard depending on what route I was taking with DPS merc's, although I must say caster merc's will do more DPS with the setup than melee