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 S&W - Beretta 92FS 9x19 Para - Rock Island Armory GI 1911 .45 ACP - Colt 1968 Detective Special .38 Spc. - Ruger LCP .380 ACP - Daniel Defense M4V1 Carbine 5.56x45 - Alpine Industries M1 Carbine .30 - Steyr-Mannlicher M1895 8x56 - Ruger 10/22 .22LR - Remington 870 Express Tactical 12GA - 1943 Izhevsk Mosin-Nagant M91/30 7.62x54R