I'm more interested in an optimal levelling route for new characters. I suspect it's to go pretty normal at MP 1 until Leorics Manor, then grind Leorics Manor at MP10 until you hit level 15, at which point with socketed weapons you could grind a little bit more of Leorics Manor, then do Act 3 at MP 10. At this stage I think Leorics Manor + Act 3 on the different difficulties at MP 10 will be the quickest levelling method (seeing as though you can be rushed to any act)
The idea is that all four acts should now have equal difficulty and value for farming, much like the original intent for inferno when Blizzard first announced it. All monsters are lvl 63 and all items, even if they have low ilvl, will roll with lvl 63 enchant ranges. Now, just because the intent is they are all equal doesn't mean it's true. If you find certain types of monsters easier to kill, then that's what you might want to focus on.
I made a quick excel spreadsheet that takes in your paragon level and gear MF as well as the % of the time you spend moving between packs not fighting anything on MP0 and calculates the increase in drop rate (aka good items over a given time frame) at each monster power. This does not factor the DPS loss caused by needing items with more defensive stats to survive the increased damage, but is close enough since the damage increase is not that large anyway.
To make a long story short, if you have a relatively high paragon level you need to spend well over 90% of your time moving around not fighting anything before it becomes worth it to bump up the monster power to something around 1~3. At lower paragon levels you still need to spend a very significant portion of the time moving around.
This shows the failure of the monster power system, at least in terms of MF. The whole reason we needed increased difficulty is because we spent too much time moving around and too little time actually fighting stuff and thus were getting bored as well as pigeonholed into builds that optimize movement between packs. Since the bonus to loot is too small, we're basically doomed to spend a significant % of the time moving between packs and still get bored and use movement-happy builds, since by definition the system encourages us to only play where we spend the grand majority of our time moving. If the bonuses were greater, even if not directly proportional to the HP increase, we might have bumped up the monster power to be more efficient due to fighting more and moving less, but currently the MF benefits are simply not enough.
There is still hope for high monster power to have a significant enough effect on infernal machine related drops, but these values and how they scale with monster power are not yet known, or at least I couldn't find any other the "100% drop at mp10" (which tells us nothing without the drop rates at lower mp levels).
Great thread glad that mine ties into this so nicely, Thank you KageKaze. (Agh I need to get to 10 posts dam URL Forum Rules)
Oh and BTW who was asking about the scaling of HP on Hell bosses regarding MP? Didn't think anyone would be interested in that data TBH.