With a full group of toons, questing should be fairly easy too.
It won't be as fast as boosting, but you'll have 4x (or 5x) toons killing, which will be fast enough.
It is a definite option to consider.








Personally, while you have the RAF, I'd try to level as many combinations as possible from 1st to 60th.
The absolute ideal would be one of every class on each of the accounts.

If you know for a fact you won't play 4x Warriors, and prefer Paladins and Druids as tanks on mixed teams, then don't level a warrior team. If you cannot stand mages, then you won't need a mage team or mages on mixed teams either.

During my RAF, I did: Druids, Hunters, Shamans and Priests.
I wish I had done: Mages and Warlocks too.

With RAF still running, I did Pally + 4x Shammies to 80th.
That amount of time is pretty much the same with or without RAF.
However, the Mages and Warlocks will be a lot slower to 80th now that I don't have RAF to 60.