OP = Original Poster
In the New York and Connecticut pizza shops I’ve been in that sell by the slice, the pizzas sit out at room temperature in display cases waiting to be reheated for slice orders, not under heat lamps.
It seems like the heat lamp would continue cooking the pizza very slowly. Maybe that would be OK.
As the other posters have pointed out, volume is going to be necessary to make selling by the slice work, heat lamps or not.
In case anybody has missed it, http://www.sliceny.com is a great resource for New York pizza information.
Good luck with the restaurant.