Camshaft plays an important role in optimal rpm range.
A stock solid lifter cam in a 235/261 has peak torque around 2000 rpm, giving best mileage/power around that range.
The late car 235 with stock hydraulic cam has peak torque closer to 3000rpm.
That's what is in my truck with stock 3 speed, torque tube, 3.55 rear and 28" tires.
On the freeways I get plenty power at 2500-3000 rpm at 60-70 mph and about 20 mpg.
My bored 261 in the coupe with the same driveline has a mild solid cam grind with the same higher than stock power band range as my hydraulic cammed 235, giving same speeds and mileage but with 50 hp more power.
When the engine runs at it's smoothest and quietest without vibrations, you know that it gives best performance/mileage with least wear.
With my cams that range is around 2500-3000 rpm on both engines.
Still plenty of hp left peaking at 4000 rpm, however mileage would go down.
