if you will shoot the 9mm more due to ammo cost I say go for it. You'll be a better shooter, and using modern jhp ammo its plenty. Personally I'm not a huge fan of the 357 SIG because I carry a 357 Mag in places where I want more punch than what a 9 mm offers (the woods). For civilian use (me) the 124 +p offers enough penetration, but if I was concerned about barrier penetration like cops would be I'd go with a 147gr.