Don't forget that both the 727 and Trident were not designed for optimum efficiency but to make very specific - and taxing - performance requirements. The '27 was built to a United requirement for a transcontinental aircraft that could get out of La Guardia (short runways, high temps in Summer) and the Trident to meet similar problems with Heathrow/Mediterranean. The ultimate Trident IIE added the RB166 lift engine (the 4th) just to do the hot weather performance with increased loads.