You'd have a 4.11:1 rear end and 1:1 3rd gear ratio.
Suppose that your tires are about 29" in loaded diameter
Calculate your RPM You would get about 2600 RPM at 55
You would get about 3100 RPM at 65
Everyone has a different opinion on the RPM "sweet spot"; I like about 2,600 RPM (for higher gas mileage and lower noise).
When my 1954 Suburban had the 3.90:1 rear end, I could travel nicely and quietly at 55-60 MPH. With the 3.55:1 rear end and all be rear bearings/bushings, I travel nicely and quietly at 60-65. I can cruise easily at 70 in terms of power, but it gets a little noisy, and my gas mileage decreases by about 1/3 (from 18 MPG to 12 MPG).
