John, what's the bake time? 5-6 minutes? If that's the case, you're producing explosive, 3 minute-ish, Chau-like oven spring in almost twice the time- and that's quite an impressive feat. To do that, your recipe and approach have to be flawless.
I need to buy a kiln shelf - my stone refused to go above 550 tonight.
If 550 is as high as your oven can muster without being modded, go with 1/2" steel plate. A 1" kiln shelf will probably pump out a 4 minute pie @ 550, but there's no guarantees, while with 1/2" steel plate, 4 minutes is a walk in the park. At 550 with 1/2" steel plate, you could easily be seeing as little as 2 1/2" minute bakes, and, if you can push the oven a little higher, you might even be able to see sub 2 minute Neapolitan bakes at 600. Maybe. But NY/Neo-NY times, that's a guarantee.