One gripe: The OP goes on about how energy required goes up with the cube of speed, but that's only true if the flights you're comparing take the same amount of

One gripe: The OP goes on about how energy required goes up with the cube of speed, but that's only true if the flights you're comparing take the same amount of time. Common sense says you should compare two flights covering the same distance. The flight that's twice as fast takes half as long, so you end up with the energy required being proportional to the square of velocity. (The power required is still proportional to the cube of speed, which is why e.g. a Bugatti Veyron costs so much.)