Hi Scot;
Its difficult to pin down energy use as there are so many variables. Size and number of pizzas baked, temperature of the product going into the oven, room temperature, and some more subtle conditions such as cleanliness of the oven. Yes a clean oven is more efficient.
New XLT ovens, Lincoln and Middleby ovens all operate for at least 30% less than the older models that are generally offered on the used market. These ovens, as far as I know, offer the lowest operating costs.
There are many other factors to consider. Consider the initial cost of the ovens, consider the length of the warranty, consider ease of cleaning, consider the requirement for regular maintenance, consider the eventual cost of replacement parts and consider ease of delivery and installation.
George Mills