Power Leveling Torment VI - 4.5 Million XP Per Minute
See youtube video I just made describing how to get 9 million XP every 2 minutes on Torment VI. Bringing a low level character along will allow you to get them at least one level every single time! Just reset the game and get your 9 million XP over and over again. I was able to occasionally get nice loot as well; in 10 runs I had one legendary. Not bad for simultaneously powerleveling someone from level 50 to 60 in 12 minutes!