Air drag increases with speed too. Air pressure at Mount Everest is, IIRC, 30% of sea level value, for a roughly 70% reduction in drag i guess, but if you're mo

Air drag increases with speed too. Air pressure at Mount Everest is, IIRC, 30% of sea level value, for a roughly 70% reduction in drag i guess, but if you're moving 5-10x faster, that's a 25-100x penalty. Airline jets fly at transonic speeds which complicates the calculation a bit but i think not in the favour of the aeroplane.