I kinda diverge from Doc when it comes to being stuck with FMJ only ammo.
For CONUS defense or police work in a full sized pistol I'd likely go with the .45 in 230gr ball. That loading is well know as far as what it does, and one of the things I have noticed is that it often actually stays inside the person shot, or if it exits it doesn't go very far.
For military work I'd prefer the hottest 9mm FMJ or AP round I can get. Bad guys who carry rifles tend to be wearing stuff, like chest rigs, LBE, etc. In testing that I have done, and seen done, or talked to other competent folks who have tested this, 9mm ball gets through things like a full canteen, loaded AK mags in a chest rig, flak vests, helmets, etc far, far better than the .45 does. IMHO any bullet hole you put in your bad guy trumps no bullet hole in your bad guy.
I also think 9mm does better against cars than the .45 does.
Also, I've worked several shootings on the street where 9mm ball was used, and the bullet obviously yawed and caused greater damage than one would excpet from a RN bullet. It doesn't happen every time, but it's rather common in my observation.
9mm bullets that yaw, example;
https://pistol-forum.com/showthread....-B-115-gr-FMJ)