For the SAA's and modern replicas, you want to stick to cowboy load factory ammo. In fact, most factory ammo I know of is perfectly safe for SAA's. The factories are paranoid about marketing anything very hot, since someone might drop a cartridge into grandpa's revolver and blow it up. For reloads, most reloading manuals will have separate, distinct sections for standard .45 Colt and .45 Colt for Ruger, T/C or carbines. For example, a typical Peacemaker load would be about 9.5 grains of Accurate No. 5 or 8 grains of Unique for a standard 250 gr. lead bullet. Those are pretty mild loads. They will throw a 250 gr. SWC at about 850 or so fps, depending on barrel length.
You can crank things up quite a bit for Ruger, T/C and modern carbines. My advice is to check a variety of reloading manuals. You'll start to see patterns develop.
