Good thread but I think hairs are being split. All of the common defense calibers can & have been put to good use. I would say that the most important thing is packing what you can shoot decent & carry comfortably. These will be highly subjective & also depend on a person's size & body type & the size of their hands.
I sometimes carry a G20 (..10mm...I've always been an oddball
). However I have had a few people tell me the grip was too big for their hands. A 120lb skinny guy will have trouble CCing a G20/21 in warm weather.
I own a 1911 but don't care to carry it. Some will carry only a 1911.
Each caliber has its fans,although I think .45GAP is a silly idea. When used effectively by a skilled or even semi skilled person they all can get the job done. One shot stops are great.....but most of us have at least 5.
As far as the penetration of this & that......if any of us (non LEOs) have to use a gun in self defense.....it will likely be real up close & not involve barriers. So I'm guessing 12 to 16 in of penetration should be good. (large assailant..winter clothing) I used the word "likely",so keep the flames to a moderate level.
One thing I will say about load selection....I like the heavier bullet weights in any caliber,even with the lower velocity. I'm a beliver in sectional density.
.45acp.....230
.40/10mm.....180
.38/.357.....158
9mm/
.357sig.....147