Jim March, you are absolutely correct. That is a good point.
Here is some old info. I have on other 158-gr. tests, FWIW:
*Handguns, July 1996, "Best loads for self-defense" by Ed Sanow. Win. 158-gr. +P LSWCHP: 890 fps; 278 ft. lbs. energy; penetrates 14.8" gelatin; .62 caliber recovered diameter (NOTE: 4" barrel length! )
*Combat Handguns, date? "Ammo vs. clothing" by Mike Boyle.
Cor Bon 158-gr. +p+ LSWCHP: 867 fps out of a Colt Det. Spec.; penetrated 19" of light clothing (cotton t-shirt) (2 of 3 rounds not recovered); expanded to .358" (no expansion); penetrated 18.5" in heavy clothing (t-shirt, heavy sweathsirt, down vest with a nylon shell); expanded to .356" (no expansion). Boyle also tested the Winchester SXT 130-gr. JHP+P : 886 fps; 11.25" penetration/.551 cal. in light clothing; 11" penetration/.559 caliber in heavy clothing.
*American Handgunner, Jan./Feb. 1998, "The Minus of +P" by Charles E. Petty. Petty concluded that only the .38 Special caliber benefits from the use of +P ammo, because manufacturers have devoted more time to bullet design with +P velocities than they have with standard pressure rounds.
Maybe someday someone will test various 158-gr. +P loads from an honest-to-goodness snubby and let us know the results???