Well, I have a stick shift, but I'll say this - 0.75:1 accomplishes little improvement and is a waste of time and money to convert. What is worthwhile is 0.5:1.

Here's what I mean. Top photo is direct drive 1:1 at 60 mph, 2,750 rpm

Next photo is 0.75:1 at 60 mph, 2,300 rpm, a savings of 450 rpm. Meh.

Bottom photo is 0.5:1 at 60 mph, 1,550 rpm, a savings of 1,200 rpm. Perfect.

This is what you get in the cockpit in real life, not what the math says it ought to be.