The Apollo Build Documents describe the Speed Switch as a shift in the speed range. It does not indicate that it doubles the speed range when engaged.
When the switch is closed it adds an additional 10u capacitor in parallel with another 10u cap. Two capacitors in parallel doubles the total capacitance which slows the time constant of the circuit by a factor of 2 or making the speed range 1/2.
If you want the Speed Switch to make the speed range twice as fast, simply label the switch positions to show the closed position as “SLOW” and the open position as “FAST”. For a momentary foot switch, use a normally closed switch for the slow mode.