Well, a pistol bullet can generally only damage tissue it physically touches (unlike a rifle). So if we look at expansion and penetration figures for a couple typical loads, we can get a pretty good idea of what a .357SIG can realistically do versus a good 9mm.

In .357SIG, the Federal 125 gr JHP penetrated 13.7" of ballistic gelatin and expanded to .59". (Reference Todd Louis Green, www.greent.com.)

In 9mm, the Speer 124 gr +P Gold Dot penetrated 13.2" of gelatin and expanded to .62". (Reference Shawn Dodson, www.firearmstactical.com.)

Now, of course, you can play around with loads and find a .357SIG that expands more or penetrates deeper. Ditto 9mm. But the results from these common, typical loads seems to support the idea that the .357SIG isn't necessarily worth the heavier recoil and reduction in mag capacity.

It's an old article, but there's some interesting reading here: http://www.firearmstactical.com/briefs10.htm. Scroll down to find the .357SIG info.

125 gr 357Sig is designed to mimic a 125gr .357Mag, it does so well. A 125 gr 9mm Para is essentially the equivilent of a .38 Spl round of the same size.

Now I wouldn't like to be shot by either. I have NEVER carried a 9mm of any kind but I have carried a 357Sig for a nember of years. Out of the HK USP Compact, the 357Sig's felt recoil is about the same as a +p 9mm but hits like a .357mag.

I now carry a 1911 in .45. I carried a 1911 before I carried the HK but switched back to the 1911 platform because the trigger is so much better than any poly pistol could ever be. BUT, if someone made an affordable 1911 in 357Sig I'd switch in a heartbeat...