Interesting observation there. Last I checked the speed of sound in air was somewhere around 1120 FPS, depending on your density altitude. There are quite a few pistol rounds that exceed that, notably all of the magnum revolver rounds, the 9x19, the .38 Super, etc., etc. Being super-sonic doesn't seem to add much to the stopping power of, for example, 9mm ball, and not being super-sonic doesn't seem to bother the .45 too much. The improved indications of stopping power of the various small-caliber pistol rounds seem more to be due entirely to recent advances in bullet design.

The SIG is a nifty little round (if someone else is paying for the ammo) but it really doesn't seem to do anything a .38 Super/9x23 (competition gun) or 9x19 (duty gun) won't do just as well or better, if all things are considered. Cost to shoot is the main gripe. Naturally, one thing government agencies never seem to consider much is cost. The ducks are always flying! (for them )