I'd imagine 5v5 would be doable with 4 warlocks + shaman (chain heal, totem of wrath, grounding totem, tremor totem (very important), etc.)

Rogues really wreck your shop, but aren't very popular in 5s.

Warrior/healer will fuck you up, and are very popular, but you can mitigate some of that with intense mana drain, and chain skillcoil.( Just remember terror has a DR now, so don't overdo it.)

I've always been very curious about mages. 5 frost mages (or 4 with a healer) would be very potent, if you are very careful.

What you want to do is get a spec to maximize ice lance damage, without frostbite, and be very, very, very careful with your frost novas. Pick a target, bust out all of your elementals, begin casting frostbolt, cast freeze ONCE right before the frost bolts finish, follow them immediately with an ice lance, if it breaks, freeze again, ice lance again, they're either dead, or bubbled. Quickly pick another frozen target, ice lance once. If you've already cast freeze twice, you have to pick a new target, this one will only sit 2 seconds in the next freeze. It really only works if you make sure to NOT catch a couple of them in the freeze until you are going to kill them.

In theory with water bolt + frostbolt + ice lance you have so much burst it's barely possible to heal through it (with 800 frost damage vs 400 resilience, this should be 20-30,000 damage.)

A very high level of control over your characters is required though, fragile characters, and placement is important.

Another possibility with the patch is subbing a hunter in for aimed shot (mortal strike shot) to really do some damage. I think this would be wise considering the growing popularity of 3 healer 2 warrior teams.

All depends on your level of control.