I have also thought about the increased wood requirement to maintain higher temps. At this point I have fired my Fontana about 5 times to cook about 10 pizzas each time. It seems I've used about 5 pieces of firewood each firing plus kindling for start up as well as kindling to increase flame when needed.
Each time there was plenty of coals left to continue cooking. I'm guessing here but if I were to have purchased a casted oven like a Forno Bravo Primavera, I would bet it would have required as much as or more wood to cook the same amount of pies. A refractory oven has more mass which requires more fuel to reach initial cooking temp.