an example using the .68 od of an A518.
3.91=2.65 and 4.10=2.78
3.55=2.41, and personally, i would feel this to be too high a gear for cruise rpm to deliver good gas mileage unless driven on relatively flat ground.
i don't know what the od ratio of the transmission wanting to be used is, but one can figure out what the final drive will be, easily.
remember though, going too low an rpm at cruise can negatively affect gas mileage if that rpm is out of the engine's efficiency range.
aero drag and weight will also play into this equation.