I used the same 10-day Glutenboy dough this week, with a couple of differences in the process.
First was that, after the dough had been cold fermenting for 5 days in oblong containers (which made it easier to form the skins for my rectangular piece of kiln shelf), I ordered a 3/4" high-talc soapstone tile from M. Teixeira Soapstone (thanks to tlj000 for finding that source). So I re-balled the dough and put it into round containers. I couldn't get the balls to close properly, and was pretty skeptical about what would happen. The dough turned out with pretty big imperfections on the bottom when I opened it.
When it hit the soapstone at 550 (1 hour pre-heat), it went crazy... puffed up like a puffer fish in places on the rim. 3 minute 50 second bake, all under the broiler. Pretty good balance of top and bottom browning. Other than the uneven puffer fish routine, it was a beautiful, tender crust with a light eggshell crunch and good crumb. This soapstone is a wonderful baking surface, almost like steel plate in results (better in my oven), and a lot lighter than steel plate (which my back thanks it for).
Next time, I will try a 6-1/2 day Glutenboy due to scheduling and see what happens to the browning.