Like I said, shoot a 125 Gr full power .38 Special (standard pressure) from a 4" revolver and then fire a 124 Gr full power 9x19 (standard pressure and not NATO) from a 4" revolver. The SP101 was offered in 9x19 with a 4" barrel.

Go to ballistics by the inch and look at the velocity for a 9x19 and .38 Special fired from a 16" barrel rifle. They have standard pressure CorBon in 124 Gr for the 9x19 and standard pressure Cor Bon in 125 Gr for the .38 Special. The velocity is higher for the .38 Special.

You do loose velocity from a revolver cylinder gap. Gases from the burning powder are expelled through the cylinder gap. A ported barrel in a revolver may increase the velocity of a bullet, but there is definite velocity loss from the cylinder gap. Find someone with a T/C Encore in .357 Mag. Fire a .38 Special round from that and compare it with the same ammo type fired from a revolver with the same barrel length.

As to performance, there is a reason federal agents used a .38 Special snub nose as a backup vs. a 9mm pocket pistol. The ammo needed to adequately penetrate cover.

Shoot what you are comfortable with. If given the choice of a 9x19 or .38 Special only, I prefer the .38 Special. I will take the performance of a blunt and wide semi-jacketed HP 158 Gr. in .38 Special (full standard power) vs. any standard pressure 9x19.