Everyone who has ever been shot and killed with a handgun "less" then a .45acp can now get out of their graves- they were shot with an inferior caliber and are only dead in pretend.
My only concern with the .45acp cartridge is that like .38 special in a snubby, from a shorter barrel it gives up alot.This is because the .45acp is a relatively lower pressure cartridge designed for 5" barrels.
In shorter barrels you'll see a greater loss of velocity then other calibers,and therefore a loss of kinetic energy and momentum necessary for the penetration that any caliber needs to do its job in order to reach vitals,irregardless of what size it is.
This is why I like .40 s&w so much.In my 3.25" barreled BMFS .40,I can launch a 180gr projectile 950-1000fps,while it takes a +P rating (and that means more chamber pressure which means more recoil in your compact pistol) for a 185gr .45acp projectile to come past 900fps from a similar sized barrel.
Not saying it won't do the job,but this is why I like .40 over .45 for guns with shorter barrels.
For the really small guns like KelTec P11/PF9 size,I think 9x19 is probably the most powerful round I'd want in such a gun.But thats personal preference.
Oh,and I'm really starting to come to the very unpopular opinion that modern hollowpoints are just as erratic in performance as their earlier model brethren when it comes to actual terminal performance in a human being.
The thing that makes pistol projectiles work is the penetration of vital structures and organs that are ultimately necessary to carry oxygenated blood to the brain.No matter what caliber your using or what whiz-bang boutique overpriced bullet; if your marksmanship comes up short of good placement and your projectile comes up short of penetration its not good.
So a compact, big bore handgun loaded with a +p round thats barely controllable for the user is not going to do as well as a combination featuring a smaller caliber and milder cartridge.
Of course,some folks are just more capable then others,so more bully for them.
But something to think about- keltec made the P11 design pistol in .40 and .357 sig for a limited time for a reason- that reason being that such a small gun was so uncontrollable for the majority of shooters that bought them that they were sent back in as being substandard guns,when in fact the guns themselves were fine- the shooters just couldn't handle them.
I think it takes a rare shooter indeed to make a .40 caliber gun the size of a P11 function well at all,let alone be as rapid and accurate as the 9mm P11.
Not all considerations for a defensive handgun should revolve around power or cartridge size.Sometimes,a compromise becomes a necessity,and I personally do not feel under gunned with my 9mm P11.