I have not, but on the FF & FC websites they have discussed this at great length. The coating on the inside is not there to 'smooth' the flow but rather to keep the heat in the exhaust gas and not transfer it to the header, to improve scavaging AND to reduce underhood temps.

Kevins description above shows the effect of this....since the gas is hotter when it leaves the header, it was hot enough to burn the paint on his muffler, where as before he coated the header, most of the exhaust heat went into the header and the gas cooled considerably before it got to the muffler.