I cannot find it right now, but there had been some cracked frames shown on the www and they cracked at the rail. It was PreB and I think not a short rail. BTW, cast frames CAN be better - as in the Browning HP going cast when they went to .40 SW - an upgrade to handle the hard hitting round.
I have imported in the neighborhood of 50 Short Rails in the last 10 years. I have ever seen one with a cracked frame, or cracked rails. I have never heard of someone saying "MY" Short Rail cracked, it's always something they heard or were told. Pre-B's I have seen pics of a couple cracked slides, right at the ejection port for the one I remember.
A friend of mine of many years and a notorious exceeder of SAMMI specs owns two handguns, an Auto Ordnance 1911 in 10mm and a Pre-B CZ75. The 10mm has a cast frame and slide, he runs it with a Shok Buff on the spring it came with, no cracking. And with some of his loads, if it was susceptible, you'd certainly expect to see it. The CZ75 is high round count (he has owned both guns for over 30 years) and has seen a few of his special loads as well, no issues.