I have the Buffalo Bore 158 gr. SWCHP+P loaded in my M-65 nightstand gun. These are loaded about 200 fps or so faster than the Federal, Winchester, Remington, etc. 158 gr. +P load. I tried shooting these in my 15 oz. 642, and it is a handful(i.e., don't count on any quick followup shots). I keep the Speer Gold Dot 135 gr. in summer, and Federal 158 gr. Nyclad SWCHP+P in winter for my 642.
Whatever load you want to carry, shoot a few cylinders to get a feel for the load.