I may be jumping in a little late but here is my feedback.
As far as wall or dome materials there is a difference. I didn't want to believe it at first but now I experienced it for my self.
The refractory bricks make a pretty big difference compare to the refractory concrete. FGM was able to compare side by side and found the bricked dome is 20 to 25% more efficient than a concrete dome. I am talking fire bricks made for a wood fired oven not the cheap fire bricks used for a fireplace.
Over all for the same walls thickness with a bricked dome, the oven heats-up faster, the natural convection is more efficient and the oven stays hot just as long.
I have had many costumers, mostly commercial user, who reported the same thing. They got to try different types / brands of ovens and after trying an FGM with the bricked dome they were sold. Some of them are now repeat costumers as they expended their business.
At this point most of my costumers take a bricked dome for the superior performance.
It is possible to cook a Neapolitan pizza in a small oven like the 700, some members can witness of that, but it takes more practice. The pizza being so close to the fire it is not very forgiving.
Ideally, I agree with Craig a 950 size oven is perfect, but I would say being able to cook with an 800 is already pretty good.
When you look at an oven, I strongly recommend to do serious research and ensure the oven you will be getting includes more than just an oven floor, dome and a sheet metal door. You will certainly start with pizza but I can guaranty anyone who buys an oven they will want to bake bread, smoke, grill, do rotisserie and much more. Just make sure it offers all of that.
Also it needs to be reputable company with BBB accreditation and so on.
The concern over, what do I do if I move is very legitimate. Having recently relocated my self, I certainly wish I could have taken my oven with me.
With the help of some costumers and forum members (they will recognize them self) I have developed a mobile cart option like the one attached. Not only you can move it around on a patio, but you can take with you no problem. Here is a picture of the last one I have put together for a client in Florida and he knows he will be moving with it.
There is also, to another costumer's request, a metal finish dome in the works. Picture of the prototype attached, just sent it to be powder coated.
I am happy to hear more suggestion on what people would like to see as it helps me offering a better product.