Ed, Speer's engineers weren't trying to make the SB load compete with high velocity .357s. They sought to get decent velocity and somewhat minimize flash, and bang while reducing recoil and bullet pull from short barreled guns all the while utilizing a bullet that would perform better at lower velocities. I suspect that they had S&W scandium snubbys in mind from the start. They did much of this by using a lighter charge of faster powder than 125 gr. screamers utilize. The pressure spike is shorter with fast powders therefore the bullet won't go as fast, but pressure should be lower when the bullet leaves the barrel. A faster powder will also require a lighter powder charge. The weight of the powder charge adds to recoil, as OKFC05 once pointed out to me. So less powder equals less recoil. The end result is a cartridge that acts much like a .38+P+ recoil and velocity-wise. I'm a classic example of the type of person that SB .357 is geared toward. I use SB .357 in my 360 PD. I can easily handle SB +Ps in my gun, but 125 gr. Remington SJHP .357s are too much. The last time I fired five rounds (I was done at that point/no mas!!!) my hand was screwed up for a month and a half. In fact, the recoil was so stout, it cracked my laminated hardwood Altamont boot grips. With short barrel .357s I'll have a good case of "magnum hand" the next day, but I'm fine. I also want to add that I'm not a recoil intolerant person. To give you perspective, I carry a 5" .44 magnum with full power ammo and it is far more shootable than a 360 with full power 125 gr. .357s.
If you put "Perma-Gel test results" into the search function, the thread I started which contains info for that load, and several others, should come up toward the top. My SB results are in the last post. Enjoy, I posted that stuff for you guys. BTW, I just bumped the thread for you. In short, I fired SB .38+P and .357 into four layer denim/Perma-Gel. The .38 didn't expand, the .357 did.