When I first got my RAF, I twinked out a couple of hunters to lvl 19. At about lvl 13, I started dragging them thru WC with my 70s. Later, I took a pair of shammies and just leveled them together, doing quests, they are now level 67. Now I don't have a scientific analysis of the leveling, but it seemed that just for gaining new levels, it was much quicker to just have the pair of "peers" questing together. Although, my little twinks have some awesome gear! LOL