I use the Old Stone I bought from Amazon. The info there says it's firestone.
My broiler has two coils, and inner and an outer. During the cleaning cycle, it cycle between the two coils. So one is always on at a given time. Cycle time is about a minute or so.
Can you tell me more about cleaning cycle causing premature breakdown (I seem to recall you used an old oven on the cleaning cycle ages ago)? How safe is the cleaning cycle hack in general? What is the worst that has happened to folks who've tried it? What are some safety precautions I can take?
James, I've never used the cleaning cycle on my oven, but my cleaning cycle light does kick on after a long pre-heat and bake at 550 (about 575 actual temp). I've never heard of anyone's house burning down with a hacked oven. I have heard of exterior elements getting so hot that they melt, but, more frequently, I've heard about wiring melting and shorting out. Oven wiring is only rated to go to a certain number of degrees (the number escapes me, but I'm certain it's below 250). All ovens tuck this wire behind insulation, but the insulation can only protect the wiring so much. From the number of people I know whose ovens have failed during cleaning cycles (regular cycles, and not pizza baking hacks), I'm certain that cleaning cycles are hard on ovens. Ovens are generally made to withstand normal baking temps without any problem, but, cleaning cycle temps push that envelope. Cleaning cycle temps once a week for pizza push that envelope even further.
When it comes to damaging the oven, I feel pretty strongly that the higher you go, the greater the risk, that's why I generally only recommend 50 to 100 degree bumps over the ovens peak baking temp.
If you want to take the oven apart and see where the wiring is situated and, if there's room, add more insulation, then perhaps you can use the cleaning cycle with greater abandon. Otherwise, if you have an oven that isn't disposable, I wouldn't push it past 650.
The Old Stone stone is cordierite. Cordierite is considerably more conductive than firebrick- hence the burning at 800. From the photos, it appears that you're not only shooting for Neapolitan, but that you have the broiler that can achieve this end.
For Neapolitan, it's really a broiler game and how much infrared you can kick out. As you found out, you don't really need an incendiary hearth, and, depending on the hearth material, you can even go with lower/less potentially oven damaging temps for the hearth pre-heat.
I'm curious when you broil outside of the cleaning cycle, do both broiler elements kick on? Is there any way of getting both elements to kick on during the cleaning cycle? Could you take a photo of your broiler? What is the vertical space between the hearth and the broiler presently?