[DPB]

I was going to say that ammo was more expensive, but I checked and it's not. Ammo price is comparable.

Assuming that .357 SIG ballistics are indeed comparable to .357 Mag (as advertised), then they are also comparable to .45 ACP. So the terminal ballistics would seem to be pretty close.

It is difficult to compare recoil, since there are few platforms that are available in both calibers. The .357 SIGs I've seen seemed to recoil "sharper" than .45s, but not necessarily harder, if that makes any sense at all.

If you reload, the .45 is a straight wall case, and the .357 is a bottleneck. Straight walled is simpler to reload, and the lower operating pressures will allow you to use the brass longer.

If you are planning to shoot a lot, here is another point to consider: .45 guns were pretty much all built to be .45 guns. Most of the .357 SIGs are built on 9mm platforms. Given that the .357 SIG operates at significantly higher pressures than 9mm, I would expect the service life of the guns to be a lot shorter, with more parts breakage along the way. Of course, this will mostly only be true with a hard use gun, and a quality .357 SIG will probably outlast the shooting 99% of owners will do with it.