I know that things are changing rapidly, but the infrastructure in Myanmar is still not the same as surrounding countries. So factor that in as far as getting around goes. Plus I don't know when you are planning to go but factor the weather in too. The tropics are not a great place for rushing around.

Totally agree on Balloons Over Bagan if they are flying when you are there. I think they only operate during high season, or at least they did when I was there.

Of course it depends on the sorts of things you like to do. I spent over 2 weeks a few years ago that did the "big 4" plus Mrauk U. But I like a slow pace.