Fill up and go like 20 miles on a highway at 60 mph with your 3.55 stop top up and come back 20 miles at 55 mph and top up which will rev like 3.23 at 60 and calculate the difference.
Hang on 273.
That puts the 3.55s pushing more wind , which is gonna take more throttle to do; so IMO not a fair fuel-mileage test.
There is a long standing ratio that says a 10% reduction in rpm, can result in a 5% reduction in fuel mileage. And vice-versa.
