Fibrament is a pretty poor conductor, but it's not as bad as quarry tiles. Well, as Jeff V proved by his quarry tile experiment, Fibrament is better than some quarry tiles, but not others. I have a theory that some brands of quarry tiles are more porous, and where you have air you have poor conductivity. Bottom line, unless Fibrament is lying about the experiment (and I don't think they are) the tile they used WAS a poorer conductor than the Fibrament. Heat IS heat. A poorer conductor at a higher temperature will transfer the same amount of energy to dough as a higher conductor at a lower temperature. Fibrament's experiment reveals what's been known in the breadmaking community for hundreds of years. The faster you can transfer energy to dough, be it by using a higher temperature or a more conductive stone, the better the oven spring. You may notice that Fibrament doesn't show any tests comparing it to other materials. That's because it would lose.
I'll try to thin the rim out next time I do this test.
What happened, Chau?
Water takes a tremendous amount of energy to change phases (liquid to gas). Dough contains a lot of water. As you increase the thickness of the dough, that's that much water that has to boil before it can become steam and do it's oven spring magic. As you go thinner with the dough, the impact of energy transfer (oven temp and conductivity) increases dramatically.
If you look at the high temp crumbs, the voids are noticeably larger. You'll also notice that the high temp (and high hydration) crumbs have greater stress fractures on the skin (revealing greater internal steam pressure). This is why bread is scored pre-baking- scoring cuts the faster setting, constricting top layer of dough, which allows for greater expansion. As you go thinner, scoring isn't necessary because there's much less disparity between the inner and outer dough temps so the rim expands much more evenly (and far faster). I think the most telling aspect of this experiment is that the only ball that didn't split was the low hydration, low temp one.
You have to go thinner, Chau. As you go thinner, the results will become much more dramatic. 'At temps of 500-700F and at hydration ratios of 65-75%' the differences will be very discernible with relatively thin (Neapolitan/Street/Elite) dough.
Regarding the difficulty you're having mixing low hydration dough, speed is important. I haven't paid attention to what your dough method is as of late, but if it's not straight (all ingredients mixed at once), it should be for lower hydration. Staggering will let some of the flour hydrate- once that happens, forget getting all the flour assimilated. Even going with a straight dough method involves some fancy footwork. Adding dry to wet helps. I've also found that quickly slicing the combined ingredients (in a star pattern) helps to let the water get into the flour without too much gluten forming. After slicing, I then mix it quickly. After it's come together a bit, I'll then knead it by hand in the bowl, then transfer it to the bench and knead it some more. I find kneading it in a bowl first creates for a much cleaner bowl and a much cleaner bench. The most important aspect of the whole process, though, is speed, once water meets flour, you have a few seconds of wetness, but after that, the flour sucks it right up.