KBrainerd, if you're trying out Scott R recipes from the Globe and participating in a forum such as this, I think you're ready to invest in an infrared thermometer.
Harbor Freight sometimes has good deals. I normally recommend a store in Hong Kong.
This is the IR thermometer I recommend for NY style baking temps:http://www.dealextreme.com/p/digital-infrared-thermometer-with-laser-sight-32-c-380-c-26-f-716-f-29079
That link is currently having problems. Here's a comparable one for $2 more:http://www.dealextreme.com/p/1-2-lcd-non-contact-digital-infrared-thermometer-with-laser-sight-50-c-380-c-35754
The shipping takes quite a while (up to a month), but the quality of products is on par with anything you'd get anywhere else. IR thermometers are all pretty cheap/made in China, but, for the most part, they generally work.
The reason I bring this up is that I've never seen a typical 14 x 16 baking stone ever do a 6 minute pizza at 525, so I think your oven is running quite a bit hotter (as sometimes older ovens are prone to doing), and an IR thermometer will tell you how much hotter you're running at and give you a better sense of what your oven can do.
I think you're also in a position to tremendously benefit from a better baking stone, but, before you go that route, I think it's best to confirm the peak temp of the oven, as that will dictate your stone options.
I'm curious, how much browning on the crust are you getting with a 6 minute bake?