None to my knowledge. A .45 has more stopping power than a 9 mm. Simple physics. F = MA
With the military prohibition of using expanding ammunition, .45 beats 9mm.
With modern defensive ammunition, for civilian use there is no practical difference.
Stopping power has more to do with hitting your target than ballistic physics. 9mm, 10mm, 357 cal, 40 cal, and 45 cal will stop someone if placed correctly. I’d be happy to carry any of the pistols in the competition.
The problem isn’t any of the weapons; it’s the procurement process. There are how many modern pistols manufactured today, and a COTS solution wouldn’t work? SF carry whatever weapon is suited for a particular job, and every one is COTS (sometimes with mods). If that’s good enough for DELTA, it should be good enough for a grunt. Spend the money saved on ammunition and range time and that will make more difference than any caliber question.
Not when it has to go through a modern ballistic plate, first.
I wouldn't give a tinker's damn for a 9mm's chances either, but at least an ap version DOES exist.