If you have engines that are "overpowered" for a given flight level, could you just build the plane to fly higher to get better efficiency than you could at a lower FL with smaller engines?
Why do huge airliners fly so low, anyway? I've read that typical intercontinental flight paths are in the FL350 to FL400 range. New intercontinental business jet usually start from MTOW at FL410 and reach FL490 at some point.
In another related aeronautics question about wings:
If you wanted to fly at M.80 speed and wanted to improve efficiency at that speed by flying higher, would the wing you build for M.80 at some higher altitude give better takeoff and climb performance than the wing you would build to fly M.80 at a lower altitude?
I understand that for slower flying, a higher aspect ratio lower sweep wing is preferable while you want a lower aspect ratio and more sweep for faster flying at a given flight level. This is because of the incidences of induced vs parasitic drag. Also, I understand that for a given speed, the higher you are flying, the more you deal with induced drag versus parasitic drag. It seems to me that airframers should be leveraging the strength of composite materials to change game as far as how high airliners are flying. Yes your pressure vessel needs to be stronger but if you can improve efficiency, low speed handling (and hence probably safety), while decreasing turbulence, it seems like a win.
I say "improved low speed handling" based on my guess that a wing designed to fly M.80 at FL500 should be better when flying low and slow than a typical airliner today that is designed to fly M.80 at FL350.