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 Python 4" .357 Magnum | Colt 1968 Det. Spec. .38 Spc. | Ruger LCP .380 ACP | Daniel Defense M4V1 5.56x45 | Alpine M1 Carbine .30 | Steyr M1895 8x56 | Ruger 10/22 .22LR |1943 Izhevsk Mosin-Nagant M91/30 7.62x54R | Remington 870 12GA