4.10's or 4.30 gears ain't going to help the fuel economy much!
Gotta know more than the diff gearing to estimate mileage. Need to also know how much OD the 10spd is going to have, where in the RPM range it's making power, and how tall the tires are before you can even begin to estimate. Tall gears in 9th/10th can make 4:10s or 4:30s pretty groovy in the bottom 8.
