GB-
I don't think anyone doubts that at speeds LESS than LRC, you really cut down on the NAM per fuel unit. You can stay aloft for a longer period of TIME, tho.
It's the "step" FASTER than LRC that's in question. IE, if LRC is M.79, then getiing it up to M.80 or .81 and then pulling back the power to LRC settings, you'll be "on the step" and get better results than LRC.