Hello to everybody,
just my opinion of Italian LEO, caliber is related to the capacity of undercover gun, the ability in controlling recoil and hitting the target under "gunfight adrenaline".
Then you can preferer the ancient school "one shot one drop" or modern school "spray and pray".
U.S. FBI statistically registred in a gunfight 3 shot at 7 meters in less of a minute.
Last but not least the cost of admunition for practice firing under stress.
So, I repeat it's my opinion, the problem consist in placing bullet in vital organs in few seconds independentement by caliber.
For duty carry, open or concealed I had only a choose: Beretta 92 or M9 in 9 Luger FMJ, with machine pistol Beretta M 12 in 9 Luger FMJ, a cheap caliber for my Agency's budget in training LEO and sufficient enough to destroy mob.
When off duty my EDC is Kimber Compact 45 ACP: 8 shot, easy to conceal and more than sufficient for self defence: bulleyes never fail.
If off duty I had to walk in "ghetto streets" I carry my Glock 26 in 9 x21 (IMI) with a spare.
I think 40 too snappy and similar in performance to 9 x 21 in FMJ version: the only version allowed in Italy
Just my 2 cent, as U.S. people like to say!