After experimenting with 1/2-inch steel plate, and stopping because the weight of it was too heavy for my back, I am now wondering if a high alumina kiln shelf would be a better option for quicker heat transfer than a regular cordierite shelf. I have located 3/4" thick high alumina shelves (claimed to have 11-12% more alumina content).
Oven setup is electric oven that goes to 550 degrees, with a broiler that will remain on even at that temperature. Not a true convection oven, but a small fan on the back wall. I'm also thinking of using a soft firebrick drilled out to fit over my thermostat to get it up to 600-625.