Just playing devil's advocate, you could have a 5/16" thick mirror and a 5/16" steel plate laying over the top of two heavily boiling pots of water for 5minutes and I got a feeling the steel and ultra-reflective mirrors top surface are going to be almost identical temps - right about 212F......... Remember that 1,500F exhaust gas stream is physically touching that header tubing there is not much if any reflecting going on. I'm real sure a 0.01-0.05" layer of ceramic coating has virtually no insulating ability at all. In other words you bolt two pieces of ceramic coated steel together and two pieces of un-coated steel together and there will be no difference in heat transfer between them.
That's not how it works, BB. Since the ceramic reflects the heat, there is less thermal transfer. So the outside of the tube does not radiate as much heat because it's kept inside. I can show this process on my wood stoves. I have the one in my house surrounded by sheets of stainless steel, which reflects heat and has less thermal transfer than steel. If I used a sheet of steel, you would barely be able to lay your hand on the backside after some time, and forget about laying it on the front side, it'll burn you. With stainless sheets, not only does the surface stay cool to the touch but the back actually stays cold. It's because of the reflective properties of stainless. The difference is substantial. I do this to radiate as much heat back out into the room as possible instead of the wall absorbing it. The ceramic coating works in the same way.
Has to be tough to dig up matching sets of headers in coated and uncoated - near mission impossible.
Since Hooker offers their headers in coated and uncoated, I'm guessing it wouldn't be that hard, just not cheap.
