I just wanted to add that the fact that it's a tuned PC gun adds value over a standard 640 IMO.
The downside of the compensated barrel guns is that it adds barrel length but that extra 1/2" - 1" is basically a big hole intended to vent gasses upward reducing muzzle rise, basicly it adds muzzle length but not rifled barrel length and a steel J frame 38 doesn't flip that much, .357 Magnum is another story.
It's still a huge bonus if you paid the going rate for a run o the mill 640 and got a PC gun instead.