"I now return you to the regularly scheduled caliber war..."
Good one, lol! I used to be part of the Church of the .45 and believed, like many, that "all real pistol calibers start with a .4)...It frosted me to no end that everybody thought those wimpy 9X19s were 'machine pistols' or something and were so great...
Then a friend of mine pulled up the FBI wound data and it pretty much confirmed what many of you here have already posted and what I've read in numerous magazine articles: with today's expanding ammo, the difference between the 'Big 3' service calibers (9/40/.45) is pretty small, indeed.
That being said, were I the person approving a caliber in a PD situation I would not choose 9. The best 9mm loads do perform as effectively as higher caliber loads in many cases...but how would I know that when I possibly left the department that the person following me would choose Gold Dots or something and not choose a less effective load that the PD could simply get cheaper?
I would look at it from the standpoint of what the worst load in the caliber is able to do....and the worst 9mm loads have a bad reputation for stopping power.