For the DH, I tested tons of build with natalya or shadow. I tested barb and wizard. I enjoyed the explosion build for wizard but I can never keep the 4 stacks of tal rasha and it annoys me.
I mainly play DH UE, and I'm much faster with it. Mainly because I have nearly perfect gear and each ancien piece is reinforced with 80+ gems. I find a bit frustrating to play T8 to farm DB. I don't play T13 either but T11-T12 are the best spot in my opinion.
I tend to say that to farm DB, just use a "speed farm" version of your most used build. The quality of your gear and the fact that you're used to this build should largely compensate the fact that this is not a "DB build".
I was very interested by all your test Bagstone, and I'm impressed by your dedication.
As a brainless build, I would advise UE with the gold belt and avarice band. You just don't use your brain for that. You run, the avarice band pick up globe and health globe, the only thing you have to do is pick up legendaries and DB. But again, I'm used to this build.
I think it's just the usual UE farm build. Something like that:
(but I use in the cube the gear that reduce by 30% the cost of fire spells, then use the fire vault. The one that reduce cost if damage free is interesting also with the other rune for even more cost reduction of vault. For passive, I get rid of hot pursuit and tactical advantage. I use ambush, cull of the weak and ballistic. If you have an amulett with another passive, that's even better. With avarice band and blood vengeance, you can vault like crazy without any discipline problem. Damage is important to be as fast as possible in the highest difficulty possible.