KenV
Aren't you understating the thrust and capability increase from the C5A to the -M model ?
It's not 'a few percent' more it seems to be more than twenty, even derated a jump from 43000 to 50000 pounds of thrust times four is a significant increase in power (like adding more than half another engine)
Plus the effect on climb rate, altitude capability and range are considerable.
Am I missing something ?