.357 Sig ballistics are nearly identical to .357 mag. The primary difference is .357 Sig is a semi-auto pistol round. One of our local SWAT officers took a .357 mag in the back. His vest stopped it, but it still left a big red bruise.
Depends on barrel length.
With long barrels, a 357mag outperforms a 357sig. With short barrels, the 357sig is the winner.
Actually, with really short barrels, say a 1-7/8” snub revolver compared to a 3”bbl auto, even a 9mm luger +P outperforms a 357mag.
Unless you are a handloader, 357mag does very poorly with short barrels.