the headers on my old SS ute were HPC coated (from new).

I was of the opinion it made a pretty noticeable difference to the engine bay heat. Also meant they clean up really well, I had the power steering pump blow the preesure pipe out of the pump body, blasting fluid all over the headers (just after a couple of full power runs on the dyno and then warming the tyres up some , so they were damn hot!). Flames everywhere and melted plastic under the bonnet but the headers came up like new afterwards..