I always wrapped my header on the four stoke and soaked a can of silicone on it, it worked awesome and held up for 2 seasons no problem. I preferred the heat not transfer back to the engine or my pants with the 450.
I love the discussion here, I was pretty stunned when CPI told me the ceramic coating was a waste of HP and not to do so with my pipe for the CR500. I'm still a tad skeptical, but I don't have a dyno and Mike does....
I also ran the question by Neil of NPP, I'll post his reply if he gives me a clear one on hot or cold pipes. I think from a mid to upper range torque prospective it makes sense that the cold pipe will have a slower sound wave and have a bit more grunt if you are jetting perfectly. If you are a tad rich or too retarded on timing, i'd think everything would fall off as unburned fuel would then get in the pipe. Without a CVT and a pinned RPM for peak HP - i'm starting to think it doesn't matter as much.
I'm likely going to insulate the stinger and tail of the chamber to keep heat of my reed block, cylinder, and pants. I'll leave the front raw with silicone clear coat and toss a carbon guard on it.