The only M1911-style .38 Super I have is a M1911 (a real 1918 M1911). I also have an EAA Witness. It is possible to handload .38 Super to near .357 levels, but it is best to use either Winchester 9x23 or Starline 9mm SuperComp brass (both of which are rimless). I have exceeded 1450 ft/sec with 124 grain FMJ bullets in mine. But one needs a strong recoil spring for such loads.

You are aware that with a 9mm barrel and magazine, you will have a dual caliber Combat Commander?