Indeed cast iron shoes make a big difference. Last year when I went back to Chama to run for a few weeks, it was the first time I had run there since the train was changed from cast iron to COBRA shoes. It took the train about a mile to heat up the shoes to where they worked well. Once warm they did well and did not seem to fade as much when they got hot. The first few sets got my attention real fast when not much seemed to happen!
Cast iron shoes grab better cold. By the time you are halfway down the hill, they begin to fade and more air is needed to hold you back. More air means a longer re-charge time, so you must be carefull.