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.
Beretta PX4 .40 - Colt 1968 Detective Special .38 Spc. - Ruger LCP .380 - Daniel Defense M4V1 Carbine 5.56 - Ruger 10/22 .22LR - Remington 870 Express Tactical 12GA