I've now leveled up groups of shammies, druids, palis and magex2/priestx2 with RAF. The first 3 are at 60, I'm working on the last one as we speak.

I boosted the first group to 40ish then quested. With the others I just quested, I simply couldn't take any more instance boosting without my brains coming out my ears. Anyway, I don't think class makeup makes a very big difference. With 2 toons doing all the single player content (using QuestTracker and TomTom etc), you kill them faster than they can spawn even if you have no aoe. I still spent most of the time traveling from place to place rather than actually killing stuff. So, my take on this is: don't worry about what classes they are, worry more about quest and travel efficiency because they will contribute a greater amount to your overall /played time.

If you can stand it, and can fill out your group to 5, boosting is still way faster. I just couldn't take it any more.