Actually, I haven't done much with .357 Mag...just too many other irons in the fire. Yeah, yeah, blasphemy, I know. As a munch of old timers say, if you can't accomplish what you want with the gun you have, move up in caliber!
My rule of thumb is if I change anything, I go back to a starting load and try it again from there. You don't have to load quite as many, but just enough across the board to watch the speeds. In a good pistol, you won't see much for pressure signs on the brass, so stick to known loads and don't try to burn the house down.
One concern you may have with those low cannelure bullets is that a loaded cartridge might not fit in the cylinder. Mock one up and try it. No one ever said you have to seat at the cannelure, but pressures rise as the bullet goes deeper, so account for that in your loads.
Go to "the Campfire" at
www.sixguns.com and you might eb able to get a little more info about loads.
Don't use the "Max load" phrase or John Taffin will cut you down in a heart beat!
BTW, have you thought about using lead?