Are we discussing insulating firebrick or thermal mass (dense) firebrick?
Jeff is discussing a dense firebrick with abnormally low conductivity. While the W-G bricks are extremely encouraging, I'm still holding out hope for something a bit lower, something that can match the lower end of the .3-.6 W/m-K spectrum that Craig references for biscotto. Unless I'm missing something, the only way that I can see a .3 W/m-K material is by adding air- and thus creating something between a dense and insulating brick. Once you enter this middle ground, though, it seems impossible to achieve the features we're looking for: abrasion resistance, thermal shock resistance, very low conductivity.
If insulating bricks are in the .2 W/m-K realm and dense bricks typically clock in around 1 W/m-K, then, if the Italians have managed to create a .3 W/m-K brick with abrasion resistance and thermal shock resistance, it's some pretty major alchemy, imo.
I brought up insulating bricks as an extreme example of what happens when you add air to firebricks- the conductivity drops, and, as the conductivity drops, you have very hot areas next to far cooler areas, which, in turn, produces thermal expansion issues/spalling. As you add air to a dense firebrick and take it in an insulating direction, it's thermal shock resistance drops.