The only time I would take 9 mil over 357 or 45 is if it was coming from a select fire sub machine gun. Its a great carbine round and a pretty mediocre handgun round. I would not say you upped your stopping power by going up in round count and down in effectiveness. Especially in cold weather where I switch to fully jacketed and hardcast rounds as 9 mil just does not cut the mustard. We would switch from MP5s to M4s during the winter months due to penetration issues. I always carried an AK47 some of the guys would carry them in the winter and M14 or AK74 in the summer. High cap does you no good if your shots are not penetrating.
Ps people of varying size and clothing are NOT the same as ballistic gel do not trust any study based on gel penetration. Go shoot a pig it will tell you 10x more.
All handgun rounds are marginal stoppers. 9mm FMJ is more penetrative than is .45ACP FMJ. Each handgun round runs from potentially lethal to potentially ineffective. Given the true effectiveness of handgun rounds I'd rather have more at my disposal than less.