Quote from aerialus
Well, my point is, this is not that easy to tell. Haven't seen any studies, good tests with loads of data proving what you say.
There are for sure certain dps breakpoints that allow higher mp. Check out 740k dps archon wizard and how fast can he do mp10. I'm pretty sure he wouldn't need to lower it to mp3 to be most efficient. It is generalization to say for example mp3 is max for best possible gear to be efficient. It isn't.
People forget about trash. Whether I'm on MP 1 or 6, it dies in a few casts, but it drops a lot more loot and gives a lot more exp on MP 6. And most elite packs aren't too bad, although reflect and extra health are a bitch, and they seem to become more common as MP level goes up. Also, the faster you kill trash, the more you are bottlenecked by your runspeed, which can't go past 25%.
With that being said, you're absolutely right, this is my supposition, and not supported by any hard data. I plan to take some data this coming week in regards to act and MP as they relate to loot and exp, and post my results to the general forum.