I went from 11-29 in about 2 hours in 60 torment 1
I went from 29-57 in under and hour in 29-57 torment 6 (and I missed the 100% exp buff)

I'm finding the second part of the very first quest, kill the witches for a HUGE bonus in torment 6, lots of slow moving melee only zombie packs. Very easy to multi-box and gain loads of exp. I will do this up to lvl 60.

Then I will consider when I'm going to buy 3 more expansions, played new expansion on one toon for about 3 hours - lvl 68, but team couldn't clear last boss (so close), I had to go to bed.