You're quite welcome, guys.

My problems with that Metalo story re: E-2 Kal-L power increase ...
1) Training to go from strong enough to wrestle tanks to shoving planets around is like one of us working out enough to be able to lift nearly the Moon. It just doesn't track. It makes more sense that he just didn't know the full extent of his strength before.
2) No amount of super-strength increase is going to result in true flight power which E-2 Superman had. Heck, he even flew/levitated a car in the Mr. and Mrs. Superman series itself while he was ostensibly 'driving' it. It makes more sense that he always could fly but just didn't realize it before.
3) One cannot train to develop whole new powers like X-Ray vision. It makes more sense that he always had these other powers only he didn't know about it.
4) No amount of training would increase one's ability to take a mere punch up to the level to take a bomb blast. And that's the kind of transition this story expects us to accept with Superman going from bursting shell levels to nuke level invulnerability and beyond. The only thing that makes sense here is he was that invulnerable all along only he never knew it.
Schwartz's explanation still is the best and covers all the above bases nicely. I'd stick to that one.
IMHO