How much power is lost through a 518

My Duster went from a 360/904/3.23 8.25 rear with a 25.5" tall tire to the same 360/A500/4.10 8.75 rear with a 28" tall tire and the mileage stayed the same but it changed the personality of the car immensely. Dropping 500 RPM at cruise is so nice, and the 4.10s wake the bottom end up too.

Cley