Hydrogen should beat out batteries in aviation. Its energy density is 100x that of batteries. Aircraft performance is much more sensitive to weight than cross-section or length, so even if planes get bigger to hold more hydrogen, it wouldn't affect their performance as much as loading up with...
We decided against the GDL 82 for the same reason (an aging KT 76). We opted for at GTX 335. Got tired of waiting for "next month" for the Skybeacon to ship.
For my 3 and 7, I do carseats and boosters in the back seat. I let them out at cruise. They can stand, wiggle, and look out the window. Mine never fall asleep (30-90 minute hops).
While speed can be converted to altitude, doing so isn't as efficient as climbing at Vy. Over a given time interval, you will always be at a lower altitude if any speed other than Vy is used during any part of the climb. Vy is the best rate of climb.