if you stay subsonic. I hear the U-2 has like 1-2kt of leeway when it is at its max altitude because if it went faster it would be supersonic but any slower and it would fall out of the sky.

To the point where, if you turned too hard, you could stall one wing tip while Mach buffeting the other.

Obligatory plug for the excellent book Skunk Works by its former director, Ben Rich.

+1, immensely satisfying read for any aviation nut

Unless you're prepared to go supersonic. Not easy to do with electric propulsion though.

Pretty sure for electric aircraft to do anything useful at supersonic speeds you'd need beamed energy. Which would be a pretty cool technology

Scimitar props are pretty tame, though, or what part do you mean is hard?