Benjammin,
I don't train to shoot center mass... And I do sometimes end up with a clip of fmj in my 229 (carry gun).
I am confident I could dispatch/render worthelss meat a 250lb maniac with less than 4 rounds of 9mm given an ideal situation as presented in your post.
I know I am not the average gun carry.. On average weeks I run 3-4 hundred rounds through my 226 and half that for my carry 229. I have my own neighborhood tactical range facility to train at, and all kinds of crazy ideas get tried out there frequently. EX firing through objects into targets, skip shots, etc... IDPA gets ya hooked... The main point is that the caliber is not what kills you.
I sincerly hope I never have to use any of my defensive weapons against a living target...
I also wonder about the scale of your perceptions of ballistic physics. How much of a blow do you think a typical man can take? Do you really think a .45 is going to knock down a 250lb dude wearing a level 3 kevlar vest? Wow! thats a lot of power... I guess based on that that I should go flying backwords when I get hit with a 12ga? Or why does my .243 not blow a 95lb javalina into the next county when I hit it square in the shoulder? Hmmm....
Must be somthing wrong with my .243...