Who keeps mentioning 45,000 feet? My mate's a 777 pilot for Emirates, the other week he stuck a photo on FB of his alt at 43k and said they only had 100 feet left and that was the highest he'd ever been since as a passenger on Concorde, and he was transiting with no pax or freight. Gaining another two thousand feet whilst loaded seemed to me to be extremely difficult.
Unless there's much of a difference in engine power...
