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