I agree with Tunnelrat in what way does the .40 have more potential than the 9mm
The same way the 10mm has more "potential" than the 40S&W.
A heavier bullet, faster, slightly bigger hole, more energy. By the standard objective measurements the 40 has has an edge over the 9mm.
This edge is only realizable if a shooter can shoot the 40S&W as well as the 9mm. If the shooter can't then the power increase of the 40 S&W makes little useful difference.