Unless I miscalculated horribly, I'm getting over 90mil XP/hr with my current spec. Noticeably over in my last two runs. Here's the run I'm currently doing on mp0:
Azmodan checkpoint to waypoint
Tower of the Damned lvl1 circle back to waypoint
Arreat Crater lvl2 to waypoint in Tower of the Cursed lvl1
Keep Depths lvl3 to lvl1 waypoint (go to town rather than going back and go the other way through lvl2 if inefficient)
Rakkis Crossing back to Fields of Slaughter, around to waypoint, end run after circling.
My last run was insane, I gained 22mil exp in just over 12 mins for just over 100mil/hr but this was probably an anomaly. It was however the first run I did with Provoke the Pack (I had mis spec'd Pride before, which is obviously a waste of a rune)
Spec: Acid Cloud/Acid Rain, Horrify/Stalker, Spirit Walk/Jaunt, Soul Harvest/Vengeful Spirit(I think this is a VERY important speed improvement over Soul to Waste. It helps for opening doors and not stopping and I have 5 up 95+% of the time anyway), Summon Zombie Dogs/Final Gift, Sacrifice/Provoke the Pack. Passives are of course Circle of Life, Grave Injustice, Gruesome Feast. (Only Circle of Life has changed since Grave Injustice was patched to become insane )
I'm only in the upper 40's at the moment as I play 5 characters and have a full time job and two part time jobs and am trying to get into medical school but this is the nicest version of the build I've tried.
My stream disconnected during the run, but I did a run in 9:00 using the above method and a Leoric's Signet. here are my results:
Run time: 9:04
Exp/hr: 96.84 million (!)
The difference between this run and the one I did with 22mil exp was that I did not do Tower of the Damned level 1 and I was less thorough on both Keep3 and Keep2 to avoid backtracking. Either way, it's very, VERY solid experience. Again, the main difference was using Soul Harvest - Vengeful Spirit over Soul to Waste. I used it to open doors so I didn't need to cast as many Acid Rains and also made elite killing much faster, as well as not having to cast Acid Rain nearly as often to kill mobs - while in Spirit Walk and Horrify, I simply cast Soul Harvest while running through a pack to kill it. This is much more efficient than stopping to cast Acid Rain while in movement speed bonuses.