The strength of the 45 case is an old rummor that needs to be burried. During a Stupid attack, I ruined a Ruger 45 cylinder, but the Win cases were fine after they were hammered out of the gun. If the 357 and 45 are both made on the same frame, then it isn't just the chamber pressure, but the bolt thrust. Chamber pressure x cross section area of the case. I emailed Uberti and they said to use only the Colt level loads. I don't know if this was the Lawyer responce or not though. Magnum Research told me the same thing about my 45-70 BFR, but I think It'll be fine up to 50ksi.

If you do decide to load on the warm side of things, I think I would pay close attention to the cylinder bolt notches. Look into the chambers into a good light and check to see if the metal is starting to push out into the notches.
I think I would pick a different gun for warm 45 colt loads though. If you don't want a Ruger, then maybe look for a Seville.