John, without actual Marsal or BP oven owners, which, unfortunately, neither this forum (nor, most probably any other forum) can produce, it all boils down to theory and eating experience, so opinions about eating experiences do carry weight.
Kelly, the reason I asked my question is that, as you go to Casey's website:http://www.caseyspizzas.com/index.html
The first image you're greeted with is this:http://www.caseyspizzas.com/images/home_03.jpg
and the first, most prominent review is this:
"Baking on a couple of modified Weber grills, Casey Crynes puts out Neapolitan-style pizzas with light, char-speckled crusts that rank up there with Una Pizza Napoletana, Tony's, and Zero Zero."
Even if Casey isn't classifying it as pure Neapolitan, on the Neo-NY spectrum, it's pretty darn Neo-y. I think you'd be really hard pressed to get this pizza out of either of these ovens. The only deck oven that can guarantee this bake time is Varasano's custom made electric Pizza Master.
Regarding firebrick and cordierite... I have retired many keyboards conveying the innate superior conductivity of cordierite as compared to firebrick, only to recently become aware that, unfortunately, not all cordierite is created equally and that it can vary tremendously in quality. Good quality, dense, non-porous cordierite IS a better conductor than firebrick, but cheap, inferior, porous cordierite may not be. And, if that wasn't bad enough, it seems, in recent years, a lot of deck oven manufacturers seem to be going the cheap/inferior route. To further complicate things even more, firebrick can contain varying amounts of alumina, making some brands better conductors than others (more alumina, better conduction). If you would have asked me a year ago to choose between 1.5" cordierite or 2" firebrick, I would have said cordierite. Now, I'm not sure.
If I were deciding between these two ovens (for NY style bake times), I would contact the companies and get the weight for the stones. Once you have weight, you have density. Generally speaking, for ceramics, less than 1.9 g/cm^3 is questionable, more than 2.5 g/cm^3 is good. Based upon my recent experiences with Baker's Pride, I wouldn't be at all surprised if the hearths clock in at around the same (or even less) density than the firebrick. If they did happen to be the same density and similar conductivity, then the thickness would make the Marsal a clear winner. But, that's only after a few phone calls are made. Beyond finding out deck weight, if the company could provide composition and/or conductivity as well, that would be fantastic, but I think that might be a bit of a long shot.
As far as bricks on the ceiling go... my vote is yes. This isn't like a LBE where you launch the pizza and then crank the burner so the blast of heat laps up and around the stone to bake the top of the pie. It's also not like a Neapolitan bake where a log is burning on the side and the heat from the flame is bouncing off the ceiling. The burner in the deck oven will be cycling on an off as the thermostat reaches the target temp, so, for some pies, the bottom burner won't be on. In those instances, I'd much prefer a pre-heated brick ceiling rather than a very thin layer of insulated steel.
But a brick ceiling, even pre-heated to 650 won't get you a Neo-y bake time. And it's not like you can move the hearth up and reduce the vertical space either. That works great in a home oven where you don't have pies to get to in the back, but not in a deck. Hitting a Neo-y bake time for the undercrust is no problem. Custom steel decks will do that and should be relatively inexpensive (the company's steel deck option is probably a boatload of cash for flimsy steel). But browning the top in that same 2-3 minutes. I'm not picturing that with these ovens.