I always use mp10 on new toons. When the enemies start to get too good, I jump out and use the AH for some big upgrades. Then go right back to 1-hitting elites.
I guess as long as you are 1-hitting elites and killing a lot of whites, you will lvl very fast.
One hitting elites on MP10? I, uh, don't think so. Even with the best possible reduced level requirement gear, this is unlikely. And certainly not before your mid 40's when that gear becomes available.
I dunno, to me, leveling doesn't take long anyway. What is it 10-12 hours to hit 60 if you are using the AH or hand me down gear, on Mp0? I really have not seen the benefit of running MP levels beyond what you can a) 1 shot whites and b) kill elites in under 10-15 seconds, unless you are specifically farming keys/ubers at lvl 60. Of course, that does not include just doing it for the challenge, which is fine. But other than that I don't see the allure, necessarily.
might wanna try a high mainstat + added damage hellfire ring on your next toon.