Agree with Jim. My first IV - 1993 came with .060. The new was "upgraded" to .093 and has lots of craze lines at the wing root. Soon, I will go back to the .060. I guess we have a tendency to "upgrade" over time, but I don't remember of a case of the thinner windshield doing anything more than the oil canning described, but I do remember reports of the thicker windshields cracking top to bottom at the wing root max bend area on at least a couple of occasions - one a close friend on a cross country. His emergency solution drill and stitch using safety wire. As far as caving at 140 mph. Not an issue as it far exceeds max speeds on a IV. This is one of the reasons I wish the IV was still available. The vast majority of current builds are 7s and there are a bunch of differences and many decisions we IV and earlier builders are contemplating are unique to those models. And, truth be told, I am still heavily influenced by an old flying buddy who built several IVs - the lightest weighing 604 lbs empty. It was a screamer as far as off airport flying was concerned. .060 Lexan weighs pounds lighter than the heat formed plexiglass.