That was the "clean" version. If it used uranium instead of lead in various components the same bomb could have had a 100 MT yield.
Yep. And it would have toasted the plane, too. As it is, they had large brass ones even to drop the "little" version.
These aren't practical weapons at that point. As someone pointed out up-thread, you get a lot more bang for the buck (sorry) from 40 1-MT weapons than you do from one 40-MT weapon. Which is why the arms race sort of stopped there.