im just after the 60-68 grind and i done it just by questing HP>Zangarmarsh>Terrok>Nagrand>Blades Edge and was about 4-5 hrs a lvl. Im not sure if thats good but i was happy with it. Just skip the nasty collection quests(remeber in zangarmarsh there are a good few collection quests that have tradeable objectives(ie.unidetified plant parts,fertile spores,bog lord tenticles,mature spore sacs) i just collected 5x amount on main and traded over to clones before handin.