When I was in the TR grind I could do 1-20 in 2 days. But please be aware that my 208 past lives is a mixture of heroic, iconic and epic. My heroic past lives is only 117.
As a sub note, with reaper out, I can do 15-30 in under 2 days ( a full weekend grind with 30%pot running). If you run like that, you will have to skip a lot of content. I did not touch GH until epic levels and when I did, I ran 5-7 skulls through all of GH and I max out my xp before I completed ToR. Great reaper do in GH 1.5k per quest. When I left for vacation on Feb 13th, I had 177k. I will be back to the grind when I get home on the 24th.
Also, I do agree with people when they said reaper XP did not have to be apart of this update, but I do enjoy the little power that is adds and hoping to be upping my game to reaper 6-8 in the next month or so.