450 is the lowest temperature I ever use for pizza (but only for deep dish). If the makers of your stone recommend a top temperature of 450, I'm guessing pretty confidently that you have a cheap stone, which will break as soon as you use it to do what it's supposed to do. You might as well push it to its limits before you have to replace it, because you're gonna have to replace it. But when you replace it, replace it with something better.
I'm not the right person to ask about what constitutes a better stone. Here's about all I know: If you get a stone from a cook store (like the ones at outlet malls), it's gonna break. Old Stone Oven and American Metalcraft offer good stones, but I'm not sure if they offer anything bigger than 15.75", which is what I have. These stones don't break, plus they hold more thermal mass than the cheaper stones.
You shouldn't have to limit your baking temperature to 450 just to protect your stone. I've put my stones in my grill many times, at temperatures that are surely well over 700 degrees. Before I knew better, I also did this with at least a few cheap stones. Those stones are in many pieces now, and they are also long gone.