Parchment payer usually indicates a safe temperature of less than 400-428 degrees. What happens if the baking temperature exceeds 428 degrees? Fire? Health hazard(s)? ......
I had been disappointed in the results of my bread after switching parchment paper brands (went from If You Care to Reynolds). I was surprised to learn that PP can have different coatings on it that can affect baking. I have been seeing lighter, softer bottom crust after baking on a preheated stone once I switched.
The health concerns with Silcone coated PP is that the plastics can leach at high temps (think BPA concerns in water bottles). With the Quilon coated stuff, the chromium in the coating can become toxic. The other issue with PP at high temps is fire hazard with the paper smoking.
In all of my baking pizzas within inches of the broilier and breads at 500F, I've never once been close to it igniting. It will definitely brown or char up if left too long.
FWIW, I don't believe that Reynold's advertises the type of coating they use. If You Care says Silicone is the way to go, although they only state baking up to 428F.
I bake my baguettes on Quilon-coated parchment paper. The deck often exceeds 500 F and the paper is in the oven for about 17 minutes. The only negative points I see are that the paper does blacken (but the bottom of my baguettes do not), and sometime the paper breaks into pieces as I try to remove it with a peel.
Quilon is FDA-approved for food contact and we each accept our own level of risk.
I buy mine in sheets from King Arthur Flour. I'm not sure about the coating safety issue, but I start my bakes hot about 550 degrees and never had it burn. You can also remove it after the steam is done with some tongs if you are worried about prolonged exposure.
Thank you to eddieruko, jimbtv, & isand66 for the answers you offered.