The technical data that HPC and Jet Hot have shown for their coatings, which I believe are similar to Cap's, certainly reduce the outer surface temperature of the headers and also reduce the heat radiated to the other parts near the headers. This means that more heat energy stays in the exhaust gas and the exhaust gas will be hotter with the coated headers. I do not recall how much, but it is sometimes advertised as a benefit, as the higher temperature means higher velocities and potentially better scavenging. Could it be enough to roast a rubberized gasket? Going to copper sounds like a good idea.
