When you try to bake two pizzas at one time, you will find that they do not bake up like they would if baked up separately. That is because the fixed oven temperature is trying to heat up twice the mass. In your case, with the perforated pans, it will take considerably longer for the pans to reach the temperature to bake the pizzas. So, it is quite likely that you will not get as much oven spring. And, if the crusts are thinner as a result, the heat transfer through the crusts to the cheese, sauce and toppings will be different than with one pizza with a thicker crust (because of the increased oven spring). To compensate for the many differences, you will usually resort to a longer total bake time and hope that the crusts are properly browned and that the cheeses are done at the same time as the bottoms of the pizzas.