I don't own a .357 Magnum and know relatively little about the caliber, but I know that the .357 SIG auto round was designed to emulate the 125-grain .357 Magnum loads like the Federal 357B 125-grain. It seems that if the 158 grain loads had more potential, the round would have been built around it instead.
Maybe that's a silly, one-dimensional look at it. I'll keep tuned to this one to be educated.
16 Pistols, 5 Rifles, 1 Shotgun, no time to shoot them