well, everyday you see all those easyjets and ryanairs at FL400 to save fuel, so flying 410 or 420 give us more direct routes, they donīt get there. I can go up to 510 certified but we do normally 390-400, i just go up in case on turbulence and long range. For 2-4 hours flight time is not worth going up and you save plenty of radiation, those G550 guys glow in the dark!!!!