The best rule of thumb is to raise MP until it causes your runs to take more than 10% longer or so than the previous MP level. If you farm an act besides Act 3, keep at MP1+, but for Act 3 you can use MP0.
In general, until you reach extreme levels of gear, MP1 is the way to farm.
You want to 1) never die, 2) basically never stop moving, 3) 1shot, or near that, every white mob.
For the most part - purely talking efficiency, MP0 or 1 = ~100k consistent DPS. MP2~3 = ~250k Consistent DPS. MP3~4= ~350k dps. This covers pretty much every gear level.
I still know a 295k DPS Archon Sorc playing in MP1 act 3.
Running only MP1 A3 when farming XP, best way to earn xp. Running with head socket and Hellfire and get around 50-60m xp / hour depending on how chatty my friends are. Sure you can bump the % of xp gained whith higher MP but what good is that if it takes you four or eight times the time killing of stuff? Do three-four runs in the same time frame as doing one with just a little bit less xp do yeild more xp and that's a fact.
Too many theories.It is simple.The best MP Is the MP you can do most efficiently without dying.For me that is MP4.Im Monk with 197K dps buffed. And I feel Mp4 is like MP1 in terms how of I kill mobs. I never die and I never stop.So I found out my MP.Find out yours.
You ask for the "fastest and most reward-yielding". In general, lowering your MP will in most cases be faster and more efficient. With your stats, you can probably do MP2, but MP1 will be slightly better in terms of loot/hour and XP/hour, maybe even act 3 MP0. However: this can become extremely boring for most people. Therefore, you should just try what's most fun for you. If you don't have fun while playing, you will not make it to higher paragon levels because it's a looooong grind and after all this is a game and not a job that you'll get paid for.
Here's an example: Jaetch with his 440k DPS unbuffed could easily do MP4+ all the time, but hit his paragon level 100 on MP0 because it was most efficient for him. However, when you're paragon 95+ it's really just about "getting there as fast as possible". Even though it's the most efficient way, I doubt anyone can do the dull grind from level 0 to 100 on MP0.
Find the level that grants you a reasonable amount of XP, but also lots of fun along the way.
I always tell people to judge it by how fast you kill elite packs. It's probably the easiest way to judge if your at a comfortable MP level.
In general, Elite packs should take from 5-10 seconds to kill. 10 seconds should only happen on mobs with whatever affixes are worst for you. So on average, you don't want to spend more than about 5 seconds on elites. 10 seconds for real tough ones.
If it takes much longer than that, you probably are too high a level for max efficiency. When I talk to people trying to farm, so many of them get blinded by the MF/GF/XP bonus, and farm too high MP. I can kill MP7-8 comfortably on my 170k unbuffed dps CM wiz.......but I still farm MP2. It is just much more efficient, I found this through timing multiple acts, MP levels, gear and builds.....
To be honest i am at 211k dps as a DH and i prefer MP3 for loot runs. But since i have been farming Para level I have been playing on MP1 and just doing act3 select spots runs. Some nights i will do 6-8 runs and get 2-7 legendary and set pieces, other nights i will not get anything. I think that if you do over 100k dps you can do MP3 for farming runs but should stick to MP1 for most things.