60-80 is kind of rough. However, when you are 10-boxing, DEFINITELY level up two teams at once. Obviously they'll be in two teams of five to get quest credit, but a simple /follow macro where one team lead follows the other does the trick. Do all your quests with them together.

Doing ten at once takes longer than doing a single 5-man team, but nowhere near the time to do two 5-man teams sequentially. There is a ton of time spent travelling and finding the right mobs that you only have to do once with ten.

Yet another advantage of ten boxing.