Tue, pistols don't always penetrate...but they will go through often enough that I wouldn't want to stake my life on it.
I have a .45 USP. I'd carry a .357 except a lot of departments frown on revolvers. They feel that 6 shots simply isn't enough (your theory on it is probably closer to the actual truth than their fishy-sounding excuse, especially since all qualification here is done with groups of 6 rounds or less). My own opinion is that if you can't hit with 6, you'll miss with 12.
J_A_B