Broiler vs. second baking steel?
I would say that in most cases neither is that helpful.  I have great success with one steel, placed at the highest possible elevation in the oven.  Preheat for at least an hour, and allow the steel to recover for a few minutes after removing the completed pizza, and before adding the next one.  I have found minimal to no improvement with a steel or stone above the pizza.  Also, in my oven, turning the broiler on, means the heating from the bottom goes off.  I also need to keep the oven door slightly ajar when the broiler is on, so I lose a lot of heat this way.  I find I don't need the broiler with my set-up.  It is less convenient for marginal gains.