Please don't stop, your posts are inspiring! It's good to have other ideas to compare. Two different propellers are a great idea. I just tried to keep it simple and use only commercially available components. You had the idea how that could be done with a twin configuration, but - without really thinking about it - wouldn't that require two full-blown motors making for some weight? And wouldn't one motor/prop suffice because the mission / drive selection is dominated by climb?

I just checked the twin with two AXI 2860/12, AXI PG4/33 4:1 gear, the Graupner 20x12 prop, and a 5s 12 Ah LiPo battery for each motor (effectively 5s2p). That is more battery than before (8s1p 12 Ah) and more weight. Now the drive's peak efficiency is at 12 m/s airspeed as is the airframe's lowest power demand. But the drive efficiency is 10% lower, prop efficiency is the same, so there's virtually no benefit. A bit more maximum height comes from the bit more battery. Climb rate is really low. It's no practical solution.

Seems it's better to use the single-drive variant (push or pull doesn't matter), put a bit more battery in it (15 Ah instead of 12 Ah), and - above all - make the airplane faster by using a less cambered airfoil. The aspect ratio could be reduced.