EDIT: THIS HAS BEEN PATCHED ON US.
I'm going to be a spoil sport for this guy:
http://www.ownedcore.com/forums/diab...5-mln-exp.html (Exploit for Exp and gold :) 2 min 9.5 mln Exp)
^ Don't spend $50 on it. It's a scam.
The 'exploit' is simply farming Act 1 Quest 3. Haedrig's Wife. Torment 6.
Accept the first part of the quest, talk to Cain, talk to Haedrig, run into the cellar, kill everything, complete the quest at Haedrig.
Enjoy.
To clarify: I do a 2 minute, 15 second run with a shittily geared Witch Doctor. I'm talking about 115k damage shitty. If you're having difficulties, or want more XP per kill, do public games. There are tons of people doing this now, so, join public games and enjoy it.