In all honestly, I have not had issues yet with leveling in WOTLK. I have done maybe 1-2 collections quests and i am sitting @ level 76 and I am in Dragonblight >.> I've done a few instances runs. I've been able to clear the nexus and UK minus the end bosses with not that much issue. This is on 5 shamans. I really think the key is rested exp and not over doing it in a session.