This chart allows you to compare the speed in MPH you will travel at a given RPM with 3.27, 3.73, or 4.10 gears.   It assumes that you maintained your Mustang's stock tire diameter.   The Max torque and Max h.p. notations are for a 1999-2004 3.8L V6.   Otherwise, this chart works equally well for a 4.6L G.T.