The "more rounds" argument is almost moot nowadays. Modern .45's (like Glock, STi, Springfield and FN) are loading 13 to 15 rounds per mag. Especially with the smaller 9mm's only holding 15-17.
NATO is regulated to "non expanding" ammunition, which makes a 1300fps 9mm into a high speed ball point pen.
The 9mm is 0.355" in diameter, in comparison to the .45ACP which measures .452 in diameter. That's a full tenth of an inch, add to the fact that twice the weight is flying in that .45 Cal proj.
Don't read from me that I'm knocking the 9mm. I love the round... for Law Enforcement... where there are no Geneva designated "Rules of Engagement"... and a 147gr Ranger T-Series will open someone up like artillery fire.
The 9mm, the .45, the .40, the 10mm, the XXX magnum +p+ super whatever, the .22 short.... they all kill you dead.
It's more of the, "what will a wounding shot do?" Especially since there are a significant number more wounds than deaths.
Personally, I'm just one tick away from trading my P220 in for a Mk25. I'd be swapping 8/10 round .45 mags for 20 round 9mm.... that's a metric shiit ton less reloads.