I broke 2 of the thinner stones (about 7/16) that I bought at the local restaurant supply for about 12 bucks. Both broke when I took the oven over 500 degF. The first time too. I had baked on both a handful of times in the 450 to 475 degF range with no problem.
I went to an Old Stone Cordierite stone and no cracking at oven max for a couple of years now. Reading up on Cordierite kiln shelves they say you can take them out of the kiln and throw them in a snow bank with no problem.
I also do cracker in a dark anodized cutter pan on the stone. If I parbake (2.5 to 3 mins) I finish off directly on the stone after topping it out.