JD, while Marc has done some trailblazing work with aluminum, I think the results are still a bit too preliminary to compare it, head to head, with steel. Right now, my gut is telling me that although aluminum makes for an excellent baking surface, it's extreme conductivity might lend itself to slightly contrast-ier undercrusts. For some, this additional contrast might be an advantage (a little more char/less golden brown at longer bake times) but, for others looking for a bit more traditional NY results, the contrast might need to be compensated for. So far, it looks like compensating for the additional conductivity is most likely achievable with formula modifications, so aluminum will probably end up being very comparable to steel.
Considering that steel doesn't require these tweaks and has a much longer track record than aluminum, it's still my material of choice for ovens that can comfortably reach 530 or higher (cut in half, of course, to make it more manageable
530, for steel, is the absolutely rock bottom for the 4 minute bake, though, and Morgan's 530 is unconfirmed, so aluminum- which is likely going to be happy at 500, is a safer bet. Below that, though, that's completely uncharted territory. 3/4" aluminum may have the necessary mass to be happy at 475, but there's no way of knowing until someone tests it.