When I lived in Dubai (read hot as next door to hell) We did all sorts of painting, powdercoating, fin polishing and not on many many custom bikes - experienced absolutely no issues. This was not on stock motors only, but highly modified hopped up machines too.
Sure there will be a debatable temerature difference discussion, however that difference is doubtfully enough to cause problems and overheating.
I used to hear that polished and chrome plated was the surface that caused overheating on cylinders.
Makes sense to me, a flat or wrinkled finish radiates heat better, and the more irregular surface is, the better it radiates heat.
Like a bare sand casting surface.
That said, I'll bet Jet-Hot coating cylinders would be a very bad idea, on headers & manifolds for cars they emphasize the fact that after coating, massive heat is kept inside and not transferred out into the engine compartment.