First off, having the heirloom shoulders (Wintergrasp Shards or Badges) and heirloom chest (Badges) each increase your experience by 10% and stack.
So if at all possible (already have a team at 80th), purchase both of these items, for each toon on your team.
I have Cloth with Caster Stats and Leather with Melee DPS Stats, figuring that will cover all teams; even plate toons in leather is decent and worthwhile for the 20% increased exp.

From 60th to 70th, you could easily boost if you had a half geared 80th.
Probably 55-60 Ramparts, 60-62 Blood Furnace, 62-64 Underbog, 64-68 Sethekk Halls, 68+ Northrend... or something similar.

Questing from 60th to 70th is quite fast, if you have a flying mount, which you can buy at 60th now.
Similarly, 70th to 80th is fast with flying, if you have 80's to buy (Account Bound) Cold Weather Flying books.