I recently became able to farm MP6 pretty efficiently. For the longest time I was using the Cull the Weak + Entangling Shot strategy, but recently invested in some new items:
Inna's Pants + Belt (both low, but dat set bonus)
Nat's Cloak (bought it yesterday, actually hindered my progression without the +10 Discipline from my old cloak....but soon...the boots...)
I'm learning that the passive skill Tactical Advantage is pretty important for farming efficiency, but I use it with Smoke Screen and not Vault.
Once I get some more Discipline, I will roll through this !@#$. Before I could tank a little bit in MP5, but now I'm going straight glass cannon. 130K DPS without Sharpshooter.
Believe me 130K dps is not enough >__> to farm mp5 efficiently(esp. for dh). I run 253K dps no ss and 187K dps completely unbuffed, and no I am not glassy. I can mp5 just fine, however It is still not as efficient as mp2 in finding legendaries per hour.
It's efficient because I can kill and move on right away. And efficient being that an elite pack should take no more than 8-10 seconds to kill (6 seconds or less preferably), unless they have shielding, may take a bit longer but anyway, you cannot do that with mp5.
True mp5 will give you more magic find than mp2 however, you get more runs in on mp2 (or whatever your "sweetspot" mp is), meaning you'll kill more !@#$ per hour increasing your chances of getting legendaries naturally.
To farm mp5 as efficiently I do mp2, Your unbuffed dps would need to be somewhere close to 300K and so on and so forth as you go higher in mp.
"Farming" mp 10 is a joke. Unless you wanna get guaranteed keys and fight uber bosses with friends, that's all I would say mp 10 is good for. By the time you get done completing an act on mp10 you'd have gotten 10 times more runs on mp2.
Efficiency is what where talking about here right? Mp 10 is by no means efficient, Not saying it's impossible, just saying it's gonna take a lot to accomplish that. (or get barb...lol jk)
Which means farming mp5 efficiently is definitely doable, it's just gonna take a lot more dps than you probably thought it would.