Before you go into all the conjecture, you may wish to do a simple time test, take off from a field, climb to x alt otw, then level.
And repeat with the level flight first and then the climb.
The key word in that sentence is "SEEM".
HiTech
Yep.

Here's another angle on this to ponder...
Consider how much time you spend accelerating in that dense seal level air before zoom climbing to altitude, vs a steady climb in rapidly thinning air to altitude. A climb to altitude is a potential energy gain, and trying to gain it first as kinetic energy, at sea level, against drag that increases as a function of velocity ^ 2, and then converting it all at once to potential energy is, well... figure it out.