Guys, Funked didn't ask about the .45, I'm sure he knows and has read about all its virtues.
I'm a .45 shooter myself, but the .357 SIG has a lot to like.
Also being a SIG distributor, I'm somewhat biased. The Air Marshalls, and the USSS are 2 good examples of units using the .357 Sig.
The major advantage of course with this round is velocity. A 124 Grain bullet will be going warp speed, in the 1400++ range. This round (well, the 125 in the .357 Magnum) is by far the best performer for stopping naughty people according to multiple agencies statistics. The SIG round replicates this in an auto is all.
Not only does the 357 sig perform well against soft targets, the added velocity also gives you an advantage against perps wearing body armour, depending on the bullet type and the load behind it. Speer Gold Dot ammo is probably your best bet.
I won't drone on and bore everyone, just check out some of the information on the 357 sig sites out there. All I can say from personal experience is that it's very loud, the recoil is a bit sharper than a typical 40 round, but less than a full up .357 magnum round from a revolver. Muzzle flip is a bit more pronounced, but Funked is a big guy, shouldn't be an issue with proper stance and grip anyhow.
The bellow is an excellent resource.
http://www.handguninfo.com/Archive/www.Pete-357.com/#Main