I have been boosting with a 85 demo warlock. I use the Felguard, then run through all the mobs using hellfire. It helps a lot to have Inferno. That allows you to move with hellfire on. a little bit of damage a few K then the Felguard mops up the rest while I gather more.

I have done the following on 4 druids at each level. no heirlooms.

UBRS/LS 55 to 57 about 40% for a full clear of 15-20 min.
Ramparts 57 to 60 about 30-40% for full clear of 6min.
Underbog 60 to current (61) about 30% for full clear of 10-15 min.

The 85 lock just obliterates the mobs. Since I am using a mobile AOE, i just keep hellfire always up gathering mobs. I have found this works better than gathering up the mobs and then aoe. I believe that hellfire divides the damage between the # of mobs, could be wrong but that is what I have observed.

The slaves just follow behind.

I only loot the bosses. The bosses go down with 2 dots and a hand of G. about 6-10 secs.

Hope this helps,

Psimoon