Although, I respect the powerful .357 SIG chambering a lot...
...I personally wouldn't want one because that power makes the .357 SIG rather abusive to the pistol chambering it. In comparison to the 9 mm x 19 Parabellum, the longevity of a similar gun in .357 SIG seems to be reduced appreciably. A Glock 17 or 19 almost lasts forever whereas the similar G31 or 32 are known to have failed/broken after only a couple of thousand rounds. Obviously, the pounding the gun receives from the .357 SIG is a lot harder.
I prefer to train a lot with my self-defense guns and I'd like to avoid my guns or a major components to break in the moment of truth as much as I can. Hence, my preference for the 9 mm Luger and .45 ACP rounds. Cost of training ammunition is another factor.
I'd give the .357 SIG an slight edge in stopping power in comparison to aforesaid calibers (9 mm and .45), though.
Alan, you seem to be well set with the more common calibers, so if you feel you want absolutely want a .357 SIG, don't hesitate. The .357 SIG just isn't for me. If I want .357 power I'd rather carry a revolver in .357 Magnum. I am quite confident you own at least one .357 revolver, too.
Best wishes!