Here is the chart:
Here are the relevant blue posts:
Make sure you read that first post closely. It indicates that bonus items can be triggered by any item dropping, where an item is a piece of gear, pot, gem, tome, or even pile of gold. It also states that the bonus item will always be a piece of gear.
So we get situations like this:
1. Piece of gear drops, bonus item - piece of gear
2. Pile of gold drops, bonus item - piece of gear
3. Health pot drops, bonus item - piece of gear
This has fairly extreme results at high MP. From here on "item" will refer to the larger subset of gear, tome, gold, pot, etc.
How frequently each type of mob drops an item varies, but we can construct a rough framework. Drops from elites aren't affected by bonus items. The ratio of elites to whites killed varies by route, but let's start with 50% of gear coming from elites and 50% coming from whites mobs on MP0. What happens when a white mob drops an item? It can be a piece of gear, a tome, a potion, a gem, or gold. Let's say 25% of the time it's a piece of gear. The other 75% of the time it is junk, but that junk drop can trigger a bonus item which is always a piece of gear.
So our number of items looks like this:
y = 0.5*x + 0.5*x*(1 + 4*bonus%)
x is the number of gear drops gained from a run on MP0
bonus% is the value found in the chart above
y is the number of gear drops gained from the MP corresponding to the bonus
If we get 350 items on MP0, we get 1050 items on MP10. Three times more.
Converting this to a percentage:
y/x = 0.5 + 0.5*(1 + 4*bonus%)
Now, let's bring in magic find. I will be assuming max magic find as it's accessible via either paragon or gear.
L = y*(1 + MF/100)*0.05%
L is the expectation of number of legendaries
MF is magic find
y is the number of gear drops gained at the corresponding MP
At maximum magic find, with 350 items on MP0 we can expect to find 0.83 legendaries. With 1050 items on MP10 we can expect to find 3.81 legendaries. 4.57 times more.
Converting this to a percentage:
L/L0 = [y*(1 + MF/100)]/[y0*(1 + MF0/100)]
Note the base drop rate becomes irrelevant. It simply doesn't matter what it is, so this percentage increase in gear drops can apply to anything: number of legendaries or number of 6-affix rares--whatever is most desirable in the loot hunt.
MP %gear with MF
When interested in maximizing efficiency, we need some sort of measure of time spent. There comes a point where increasing dps no longer increases the speed of clearing the map: travel time. It takes me 15 minutes to run through most of the maps in Act 3 on MP0. It takes me the same 15 minutes on MP1. If there are 0.83 legendaries per run on MP0, that is 3.32 legendaries/hour. In order to surpass this rate, we have the following time limits:
MP Time limit
Even if it takes twice as long to run MP5, it is still more beneficial for loot than running MP0. It is not necessary to "one-shot" mobs to be efficient.
As a percentage of time, it would be identical to the "%gear with MF", so if the MP0 run takes something other than 15 minutes, the percentages two tables up can be used to calculate matching time limits.
Lower monster power will always be better for xp, but higher monster power is better for loot, due to bonus items. Exactly which MP is optimal will vary by the class's movement speed and the character's gear.