I make it more like 33%: If the diff pinion is rotating at y RPM, then the wheels with a 4.7:1 axle will be spinning at y/4.7 RPM, and the wheels with a 3.54:1 axle will be spinning at y/3.54 RPM. The percentage increase in speed will then be 100*(y/3.54 - y/4.7)/(y/4.7) =...