The Gen 4 GLOCKS seem to have fixed the light mounting problems with their stiffer recoil spring, so that will not be a problem in the future.
I like the technical info on sectional density Fred, but there is no such thing as a 105gr .357 sig doing 1600fps in the real world for us to purchase as far as I know.
The ft/lbs are not that far apart even given the seemingly wide difference in number you give for velocity according to sectional density.
125gr .357 = 584 ft/lbs
135gr .40 = 567 ft/lbs