I base my analyses on personal experience from behind the trigger. Never could I tell any deference in the 9mm .45 acp. Few individual in the military really need to carry a hand gun, anyway. Maybe, some individuals in the Division or Corp TOC The General, G-1, G-2, G-3, G-4, and the SGM's. The various verisons of the M16 do get in the way. Each individual has their own opinion on this topic of big vs small and fast but very few of those with opinions have been behind the trigger of both rounds. If big round really did knock people off their feet then my .50 cal gunners would have had to go into the next county for body counts.
Yes, I understand statisics, really well, I know Confidence levels, can work Chi Square and three way analysis of variance without a calculator (taught the under graduate course at the university). The average 11B has no need for a hand gun and any NCO or junior officer should take take contraband weapons away from the soldier, for safe keeping, when they find them.
As far as any military hand gun, even for the brass and without thought to the caliber, it needs to be GI proof, meaning few, big (no little parts), simple parts that are difficult to lose, break or go home with the soldier. It also must go "BANG" each and every time you pull the trigger (much more important than caliber). Mag should be near indestructible and go in gun easily and quietly in the darkest of the night and the worst of conditions. Mag must load rounds into the mag easily, without tools.
This is not to put anyone down these are from my personal experiences