I am by no means a cartridge mechanic expert but as far as pressures, the 38 super is compatible with that of the 357 mag. The bullet diameter however, it is different. The 357 mag bullet diameter is 0.357 inches while the 38 super is more in line with the 9mmP, which I believe it is 0.355 inches. The 38 super being 0.002 inches smaller in diameter actually helps to reduce the pressure.
When you shoot 38 specials in your 357 mag revolver, make sure you clean the chamber well so the 357 mag can be chambered later; otherwise that will create some high pressures or simply prevent you from chambering. I would have to assume the same thing would hapen if you decide to experiment with the 38 super.
Camba