IMHO, 120+ mph with 1.5 hr duration all packaged into a 70 kg empty weight plane usable by the average pilot is defying physics as we currently know them.
Edit add: I would be thrilled if you could prove me wrong.
I think we are closer to that day now.
I think I got it now. 12.8 aspect ratio. No LG hanging in slip stream.Anything efficient will have a decent L/D ratio. Biplanes don't.