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I cook successfully at 700, with 1 1/4" copper couplings providing space between the plate setter and the stone. I never really toasted my original gasket, but it was getting brittle, so I installed one of the new Nomex(R)gaskets.
IMHO, if you want to cook that hot, you need to use a homemade dough with 60-65% hydration.
I am going to go back to 600-650 next time, just because it works and it is easier not to overcook the pizza.