I'll skip quoting all the "Prince Valiant" stuff but I do have to take exception with it.
He did lots of work with numbers to show his theories. The real world blows a great big hole in it because torque production is not linear. Efficiencies of individual parts vary greatly with engine speed. The whole package will swing widely as the engine accelerates through the rpm range.

As for super stupid-low gearsets, you're killing your mileage.
How many of you have a 2.2 or 2.4 geared M-body that gets better than 15 mpg in the city? It doesn't happen because the car has to work so hard to overcome the lack of torque multiplication during acceleration.
Seteady state cruising is great but you've got to get up to speed first.