no matter how much dps you have...
mp0-1 will be much faster than 5+
anyone that farms mp5+ quickly would obviously farm mp1 faster... some simple math dictates this...
so, if elite execution speed is the only criteria for efficiency then high MP is not efficient, however, this is not the case
as some people here have already pointed out, the efficiency for high MP involves not dying much, and not wasting too much time kiting around senselessly, which leads to faster elite execution but is not itself the same thing.
i have pretty average gear (no nats, legacy or new) and i farm keys on MP10 in about 30minutes, i am not suggesting this is 'efficient', however i do have fun playing on MP10 as it is challenging, and i guarantee key drops, i used to farm keys at mp7 in 10minutes... but i got tired of doing 2-3 runs without getting a key to drop, so i just push the MP up to 10 for keys
because i find this game very simple and boring, i usually do not even play on MP lower than 5... i know it would be significantly faster on lower MP but i would get bored after 5 stacks...
video of my bad DH farming keys on MP 10 here... ;)
http://www.twitch.tv/philosophios/b/340113559 (skip ahead to about 39minutes, my first run was with a random DH who i dont play very well with)
here is a shorter video of MP10 on DH w/o nats... http://www.twitch.tv/philosophios/c/1731631
You sir, are a legend!
I just ran your build with a group on MP9, higher than I've ever been for farming and I did alright with it. Still took a few deaths but I was out-tanking our WW Barb at times. Absolutely brillant build.