Dirge
Defiler
Warlock

And with that makeup, you are effectively a RAID Main Tank Group. I run the same 6-box setup, but I have a Guardian instead of a Zerker. With this group, there is literally nothing in the x1 scheme of things that you cannot do. In fact, once you get your epics, t2 shard armor and 150+ AA's, you should be able to take on lvl 80-83 x2 mobs with little trouble.

Yes, DPS is low, but survivability is HUGE. You really have to try hard to fail with this team. Things won't die quickly, but they will die.. and when you walk away from the fight, you'll generally be at full health and 90% power and running off to find other things to kill.

When I 'quit' last month, half the reason was I felt I 'beat' the game with my 6-box team. The only thing I hadn't done is tank a T3 or higher Raid, and honestly, I doubt i could do it with all the movement involved in some of those fights. If you want to 'beat the game' this setup will get you there.

Make sure you spend your AA's on all the skills that make your team(group) better, instead of say... specing your warlock to solo w/ Wards and roots. There are other routes you can take, but they won't be as efficient as the above (just my opinion).

g'luck