I boosted 4 druids up to 70. Ramparts and mana tombs are both good up to 65. Clearing UK up to the first boss can be done at level 65 til 68 or 70 when questing in northrend might be faster.

I had all 4 of my druids putting HoTs on me and keeping me topped off so I could grab huge pulls without stopping. I did mostly only rest XP but it wouldn't take that long without it just to get to 68.

My level 80 team I didn't do any quests except instance quests and a few of the starter northrend ones for good gear upgrades. I leveled by clearing instance after instance. Best part about doing it that way is you will have all the best gear possible for your level. I dont think I had a single green since about level 73.

This is a sort of casual approach to leveling though because you only get a level of rest per week so it will take you 10 weeks to get 70-80. If you play more than 1 team at a time you will never run out of rest on both of them in the 70s.