bigjae1976: With our ceramic coating experiences, we've tested surface temps of manifold tubing while loading the vehicle on the dyno and have seen temperature differences of over 500 degrees. That data is used to reference radiant heat in the engine bay.
As far as the metal failing; ceramic coating is applied to the inside of the manifold as-well as the outside. Doing this reduces the heat transfer into the tubing, which increases the life-span for heat cycles. How far or long, we haven't had a controlled test to gauge these specific results/comparisons.
E85head: We have a few different vehicle setups that are getting fitted with our Tubular Manifolds. We will be quick to share results as the cars come back together and get re-tunes!