Jusapena, how close are you baking the pizza to the broiler? If there's any chance of top leoparding, the pizza has to be within an inch of the broiler. Even, then, though, only about 1 in 300 ovens has the power to do leoparding, so the odds are not good that your broiler is strong enough.
If you want charring on the undercrust, there's a chance you can get that at 500 with thick enough aluminum plate- maybe 3/4". How hot is the steel getting? Many 500 deg. dial ovens can reach 550 and higher. If you can hit 530 with 1/2" steel, you can definitely get some charring on the undercrust.
With the advent of steel and now aluminum as baking surfaces, oven mods haven't been discussed in quite some time. If your oven is one of the few 500 dial ovens that can only reach 500 or lower, then you might want to think of a trick, such as the frozen towel technique.