38spl data works just as well in a 357 magnum case as it does in a 38spl case. 38spl +P load data is good for a bit of kick but still still very shootable.
Depending on who made your lead bullets they may be good all the way up to full 357 magnum velocity. Swaged bullets you should keep at 38spl velocities but most hardcast bullets are good to go for full power loads.
New gun, same ol' shot.