Boosted answer in a bit of a snooty-ish way IMO. The heat has to go through more/thicker surface to escape, the amount of "extra" heat retained would not effect a
Engines performance in any meaningful way for 99% of use in the world.
Top engine builders are not concerned with there engines looking stealthy/stock or even pretty with painted parts.
To make a blanket statement of
Painted or powder coated intakes or other parts as a power hindering problem is not only uncool, but certainly show stupidity on the posters behalf.
Making a reference of compare to top race builders/teams engines on relation to our very (by compare) mild engines is an insanity at it's mildest with true adjective words escaping me.
While there is a scientific way to up hold this, to think it would hurt/hinder engine performance in a detramental way for us street and mild race guy is CRAZY!!!!