MP0-4 is to grind paragon levels
MP5-9 is to find gear
MP10 is to get 100% keys/organs, for anything else it's a waste of time
Not really... you can find the same gear at MP1 and if you're steam rolling clears you're finding more loot at a faster pace. I dropped down to farming MP3-4 and im finding a lot more items over that time span. It ultimately boils down to how fast you're clearing the runs . As you level higher in paragon levels you can drop down to a lower MF level to scale your overall MF if you so choose. Thats why most people that I've seen hit 100 para just go to MP1 and clear shit pretty much instantly.