Act Five Experience Completely Wrecks Game Balance! Wow, whodathunkit.
Oh, wait. We've known that since the second week of the Beta over two years ago.
Too bad there isn't an option to Say No To Act Five. Oh wait, that exists, too! And I found out how to do that almost two years ago, as well.
I always wanted to try what you did, though: a full uninterrupted run. Came close a few times, but never did all four acts in one chunk.
Can't leech off Diablo? Does that make him more challenging, or merely more time consuming? Blizzard is actually screwing with experience penalties for high level chars again? Instead of actually fixing the game? My oh my oh my, do not even get me started.