According to this page:
Experience awarded by level 61-63 monsters has been increased by approximately 60%
and
The drop rates for high-end items (items level 61-63) have been
increased for Acts III and IV of Hell difficulty and Acts I – IV of
Inferno difficulty The new approximate drop rates are as follows:
Hell – Act III and Act IV
iLvl 61: 9% to 13.9%
iLvl 62: 1.9% to 3.45%
iLvl 63: 0% (no change)
Inferno – Act I
iLvl 61: 17.7% to 23.9%
iLvl 62: 7.9% to 12.6%
iLvl 63: 2.0% to 4.8%
Inferno – Act II
iLvl 61: 18.6% to 23.3%
iLvl 62: 12.4% to 18.6%
iLvl 63: 4.1% to 9.3%
Inferno – Act III and Act IV
iLvl 61: 24.1% to 27.1%
iLvl 62: 16.1% to 21.7%
iLvl 63: 8.0% to 16.3%
Also, don't forget that One key detail is that Monster Power grants very different bonuses and changes while on Normal/Nightmare/Hell difficulties, compared to Inferno difficulty. For the first three difficulties, while characters are still leveling up and not yet finding end game quality gear, the following changes can be enabled.
(source)
And this one: Players should now encounter more monsters in Acts I, II, and IV in Inferno difficulty when playing at Monster Power 1 or greater
(source)
Here are 2 tables with the effects of Monster Power(both pictures taken from DiabloWiki
):
So answering your questions:
- Even at MP0 you will get better loot in Inferno than in Hell(as we know, even MP1 buffs all monsters in Inferno to level 63, so try to play with at least MP1 for much better results)
- Didn't find any information about that yet
- You may get more XP per enemy killed at Hell MP10 rather than at Inferno MP1, but you will encounter more enemies which will lead to more kills and more overall XP.
And if you can do Hell MP10, I assume that you can also do Inferno MP3-4. If it is the case: go to inferno!
Hope it helps