If I were coating the exhaust and expecting the coating alone to do the job... I'd lean toward the Swain Tech Coatings
and DPR (Dan Paramour Racing)
White Lightning Zirconium Dioxide based ceramic coatings on the header and intermediate pipes. I'd use the thinner Jet Hot coats on the muffler. The Ceramics are laid on at .015-.020".
The Organics like Jet Hot are laid on at .002" similar in appearance and function to a super high quality paint. These coatings will stay bonded to the parts and provide exceptional corrosion protection. The thinner layer, in theory, should not be as prone to thermal shock cracks. The downside is less thermal protection.
The Ceramic coatings are not as aesthetically pleasing but the thicker layer provides more thermal protection. In theory the heavier coating may be prone to thermal stress cracking but in practice it doesn't seem to be a problem... drag, road, and track racing is not done in wet and muddy conditions and mudding is wet from the get go avoiding the potential of going from dry and hot to large amounts of water being splashed on the headers.
The rules of the Universe say that eventually any Ceramic or Organic coating will heat up to the substrate temperature. They just slow the progress. That' just the way it is unless you have access to real magic.
A layer of insulating header tape should keep the heat in and the cold away from the parts to prevent thermal shock cracks and separation of the high priced coatings. It's probably cheaper to just wrap the pipes and buy a new set when they rot out.