I agree w/ investing in the 357 cases -- if for no other reasons than it takes the guesswork out, and removes even the faintest possibility of using high-pressure loads in a low-pressure gun.
-- BUT --
Case strength (38Special vs 357) is
not the issue in a
revolver. Both cartridges are fully supported all the way back/past the web to the rim itself. Pressure capacity is therefore determined by the steel cylinder wall, not the brass case wall.
(Might get
interesting in a lever-action
rifle, though, where some small portion of the web might be unsupported and/or the chamber/head area given some slight extra clearance to ensure reliable feeding. Below is a pic of my heavy-load 45 Colt cases used in a Marlin.
My 357s exhibit the same in a `92Win. I just two-stage size them both and go on....)