I haven't worked with the 357 Sig cartridge and have wondered how good a service round it would be. For defense, I carry a S&W 340 PD, 357 Magnum. If the bullet doesn't kill the perp, they will have heart failure with the flash and the report.
My other concealed pistols are 9mm, 45 GAP and 45 ACP, I have problems with carrying concealed, I am 5'7" and 145 pounds, only during the cooler seasons can I carry a large or even an in between sized semiauto. During the warmer months, the 340 does me well, it is a Scandium and Titanium so it will not rust from my sweat. The barrel liner is Stainless Steel.
If you carry, really practice regularly and there is no fixed distance, so use 5', 10', 15' and 20' as your distances, shoot one hand and with two hands. Here is the hard, shoot with the parallel and close to your chest.
Most people find it difficult to shoot accurately at 3 to 5 feet, but your close enough to cause fatal damage with one or two hits any where in the chest. Every 4 or 5 years I take the NRA Basic Pistol training just to get a refreasher. I try to practice twice a month.
Jerry