I''ve seen the old "a 9mm HAS to expand to work but a 45 doesn't" thing way too many times. So a 9mm at .355 caliber absolutely has to expand to the magic .45 or bigger or it just won't do the trick huh? That .10" is SO critical it makes all the difference in the world does it? A heart, brain, CNS, bone, etc.......can all tell the difference? I swear too many people believe if a 9mm doesn't expand it just evaporates as soon as it touches your skin. Then on another thread a HUGE percentage of people will say they only carry ball because penetration is the only thing that matters. I've done a TON of reading on the subject and the only thing I've concluded is that there are few conclusions to make other than SHOT PLACEMENT regardless of caliber is king.
That being said, I prefer to carry my M&P 9C with 13 rounds of 9mm. I usually have a spare magazine on me and a fullsized spare in my car. I can't imagine the circumstance where I would be in any situation that I would say, "if only I had less ammo with me." I can, however, think of many scenarios where I would wish I had more than 7-8 rounds.