Still sounds like you are talking about the metal by itself. That's not what I'm talking about.
Brian, if you have aluminum on top, for a portion of the bake, it would be like baking on only aluminum. The pizza would cook at a highly accelerated aluminum rate until the aluminum was exhausted, and then it would cook at the slower cordierite rate.
I guess if you went with an exceptionally small piece of aluminum, you could get a quick burst of heat and then you'd drop to the cordierite speed, but I'm not sure how much thermal mass a small piece of aluminum buys you.
It would be ideal, though, to, rather than a burst of heat and then a drop, to have something more constant. If you put steel on top of aluminum, you'd get a steady steel rate of transfer for all the energy in both plates.