Why stop at 68. 1-60 again would be painful. Keep trucking from 68-80, it is not that slow. mix up the questing with instance. Don't forget to level gathering + enchanting along the way. The true pain would be to have 10+ level 80s and realized you have 0 professions on them and go back to level professions.

The key here is not to get burned out. and focus on 1 group at a time.