You know what. .40 has a fairly impressive history of stopping threats.
You know what .45 has a fairly impressive history of stopping threats.
You know what 9mm has a fairly impressive................etc.
You know what they all suck without a high quality bullet loaded into them. (HP etc. )
You know what even with the best performing ammunition they all really just suck less. If you think a single piece of tiny lead is going to stop a determined attacker barring the perfect shot that hits the off switch then I think you may be under some false hope.
Any of them work about as well as the other and differences are in the statistical noise. There might be slight pros or cons here or there ie barrier penetration, flatter trajectory, capacity etc but again none that hugely outweigh another.
One of, if not my favorite piece of tactical Tupperware is the HK P2000 in .40 caliber. I give up 1 round to the 9mm or 3 rounds to a Glock 19. I give up 1 round to a Glock 23. Recoil is very manageable and equal to or lighter then a G19 with proper defensive ammo. Honestly you could give me either a G19 or a 23 or a P2000 or a SIG P220 and as far as I am concerned the most striking and appropriate difference is how the triggers work/feel.
I think the most telling thing is when you look at the ballistic performance of the HST line they all 9mm and above perform eerily similar almost, dare I say, like they were designed to.
Pick what you like and to quote one of our fallen brothers BA/UU/R. Don't sweat the small stuff. Variety is the spice of life and when there is a shortage those of us who have and are comfortable with all the major calibers are likely still hammering away at the range while the dedicated 9/.40/.45/God forbid .380
shooter is likely staying home due to lack of ammo or fear of depleting the stash.
But as long as we are on the subject.
.45
Ak
Maryanne
Chevy
Windows
New battle star galactica.
I think that covers all the answers.