4 DKs + Holy Pally / Disc Priest is most popular for what you mentioned you'd be doing. In terms of support on setting up the team, they're also probably the team that has the most threads on DB on HOW to do it.

You'd be surprised at how much survivability an Aff lock has. I roll a holy pally in a traditional 5s team and my healing after about 3 minutes was only marginally higher than the aff lock in the enemy team! I was silenced and Ccd a bit but drain health is amazing! I role a 3 demo lock team and they're fairly OP in BGs. If you're doing a 40 man CtA then aff locks are the way to go.