I don't even think quadcopters could produce 20% thrust at that height... which is pretty bad as consumer quads have something like a 2:1 thrust/weight ratio, m

I don't even think quadcopters could produce 20% thrust at that height... which is pretty bad as consumer quads have something like a 2:1 thrust/weight ratio, maybe 3:1. High quality racing quads can get 8:1, but those have tiny batteries.