Doc,
since you raised the issue of defensive pistol performance and it does relate to the discussion in general, what are your thoughts about the defensive pistol bullets and rounds?
I won't get into too much detail here, as I'm not sure it's the correct forum. I must be clear that I am NOT a ballistics expert; my area of study is more on the "software" side of things (training & mental aspects of DUG's and OIS's) rather than hardware.
But let me say in general that for serious social purposes any of the standard service calibers (38 Special/9mm, 357 SIG, 40 S&W, 45 Auto), when loaded with any of the premier JHP bullets from Speer/Federal (Gold Dot, HST, etc), Winchester (Ranger Talon, etc), Hornady (TAP, etc), or Remington (Golden Sabre), will get the job done provided your shot placement is correct. If you want to carry a non-police caliber such as 357 Magnum, 41 Magnum, 44 Special/Magnum, 45 Colt, or any of the 45+ Loudenboomers, you can find good JHP ammo for it as above, but game-hunting bullets aren't necessarily suited to shooting people for reasons that become obvious when you study the anatomy a bit. There is other good ammo out there, but there isn't time or space to go into all of those here, even if I cared to or was qualified to do so.
But let me say this, most emphatically:
training is far, far more important than choices of gun or ammo, and 90% or more of handgun owners completely blow this off. Taking a quality 3-day defensive handgun/rifle class from a quality instructor is far more important than buying up a crate of the "best" ammo. Thunder Ranch, Gunsite, Massad Ayoob Group, John Farnam, Tom Givens, Henk Iversen, and a number of others offer quality instruction at a very reasonable price, considering the value of the instruction offered. Shot placement is the wild card in mano-y-mano stopping power debates, as there is all manner of nonsense about that on the interwebs. Shot placement is part of what I train people in doing through Tactical Anatomy Systems LLC, and all of the instructors I've named have very good knowledge of that subject area; this is not something that can be adequately put into words on a gun forum.
For in-depth reading on hardware, I'd recommend you look up Dr. Gary Roberts' work on sites such as this one:
https://www.ar15.com/ammo/project/Self_Defense_Ammo_FAQ/#mozTocId912099Start there if you like, and extend your search to find the most recent info. Dr. Roberts does regular and extensive ballistics testing through his roles in LE in California and as a military reserve officer. His work is broadly available on a number of websites and forums, as he shares the general results quite freely. He also has access to enormous databases of real/street shootings, so his bench gelatin tests are published with consideration of the effectiveness of the ammunition's performance on the street. So when Gary says a particular load is a good choice in our snub 38 revolver, but another load is better in your long-barrel .45, you can pretty much take that info to the bank.
