I've found that MPG gains are always improved most by dropping RPM.
I guess that Piper had a flat 6? Thats a 300 combustion cycles per minute drop in fuel use. Having pitch control on the prop was a huge advantage, since you could adjust the load.

I found MPG in an adjustable PCV valve. My 99 Dakota with the 5.9 dropped more the 100 RPM at idle, and that helped city mpg quite a bit.
The OEM pcv design is inaccurate and inconsistent. I put one on my 73 Ford and the adjustment range let me set the idle at 550 to 600, and it gained around town as well.

I wondered how a Magnum would do with a well programmed 8 speed, so that cruise RPM could be held around 1800 or so