In standard factory trim, think of the .38 Super as a 9x19 +P+. You can get pretty good ballistics out of it without pushing past the red line, like 125's at 1300 fps.
Some factory ammo will be lighter than that, a few hotter.
If you want to push past the stated max to make Major for competition, there are some limitations. Mechanically, you should have a ramped barrel for extra case support. Your brass will last longer if you do.
You should get a barrel (if possible) with as tight a chamber as possible, to minimize expansion and sizing work, which leads to brittle cases.
In competition, you can't use the .38 Super at Major unless you shoot in Open, and even then must have a supported (ramped) barrel. If you want to shoot your Super as an uncomped, non-optics gun in Limited, you can't shoot Major. (You might as well use the wimpy loads then, 125's at 1050 fps)
It will be an accurate gun, and in light loads a creampuff to shoot. In Major it will be loud and have stout recoil.
Ammo costs are comparable to .45, unless you're loading Major, in which case the cost goes up due to costlier components and more powder.
Example:
.45 200 gr lead, 4.5 gr powder, primer
.38S (minor) 125 lead, 4.2 gr powder, primer
.38S (major) 125 jacketed, 9.5 gr powder, primer
The jacketed bullet and double the powder use cost more money. But, you can load jacketed bullets and slow-burning powders in the .45, too.
For all the noise and velocity, the Super is still a marginal hunting cartridge when you approach deer-sized critters,
[This message has been edited by Patrick Sweeney (edited 07-13-2001).]