Gmc, the .357 Sig is, in my opinion at least, a very excellent round. Indeed, I often carry a Glock 33 in that caliber. To equate it directly to the .357 Mag, however, is rather misleading. It is true that the original idea behind the development of the round was to create an auto cartridge that would compare favorably in performance with the .357 Mag revolver round. To a degree at least, they succeeded. Essentially, the .357 Sig is a .40 Smith and Wesson cartridge casing bottlenecked down to take a 9mm (.355) bullet. What you end up with is a sort of ".40 S&W on steroids," so to speak.
The bullet (usually a 115-125 grainer is used) will exit the muzzle at somewhere around 1350-1500 fps. Thus you have similar performance to the .357 Mag round. It is a most effective man-stopper. Here is a sight that will give you about all the info you will ever need on the round:
http://www.handguninfo.com/Archive/www.Pete-357.com/