Loading manuals are full of .38 Super loads. Unique is a good propellant for factory load duplication. However, if you are looking for really hot loads, see if you can get some 9X23mm Winchester brass. It will work well in the .38 Super chamber (but is rimless, whereas the .38 Super case is semi-rimmed). This case is extremely heavy and strong. A load of 8.6 grains of AA #5 behind a 124 grain FMJ 9mm bullet and using small RIFLE primers will get you about 1400-1450 ft/sec depending upon your barrel length. But you should use a heavy recoil spring in whatever pistol you have.
I have loaded and fired many such loads in my GM, and they are a handful. DO NOT use .38 Super cases for those, only 9X23.