Ditch the Caputo. It's meant to be used in ovens that operate at 800+ degrees. Caputo has recently started making a flour called "Metro" that is made to be used with ovens that operate under 700 degrees. I don't think that anyone here has used it as of yet.
In any event, your oven setup is not going to produce a Neapolitan pizza with or without steel. It may be advisable to move on to another style of pizza that's more compatible with your oven.