Quote from Loroese
There are 3 main parts to progression: XP, Loot/gold, and high MP.
If you're just trying to farm XP, then you don't need to worry about upgrading gear and you run lower MP as fast as efficiently possible. You just repeat until you get to plvl 100.
If you're farming for Loot, you're going about it the wrong way, imo. The key to loot is MF. The higher your MF the more legendaries you get and the more high affix rares you get. If you're running below the max MF you're hurting your potential for loot. Some of this is offset by the MP level, but at MP5 you only get +125% MF, and the cap is 300%. Instead, you could lower the MP and equip some MF gear so that you have the same general clear time for a given run. That will increase your drop rate of rares and legendaries because of the extra MF.
High MP progression is similar to loot progression because you'll need good items to progress to higher MP. To get those loots without using RMAH or flipping items, you need to be able to farm efficiently. This is usually better suited for higher plvl players since the base MF from paragon level, combined with the bonus MF from high MP, can make it worthwhile to start farming higher MP for loot. Higher MP also implies Ubers, which are best to farm at MP10 because you get a ring each clear. However, that requires higher level gear, which you have to find or fund somehow. Generally the MP can be raised slowly as you improve your gear with the ultimate goal being MP10 farming and Ubers.
Forgot to mention this; my gear is equipped with MF on it (besides a ring) my total with NV is 227% and maxed with NV. it's even more with the 5 MP.