header wrap or not?

If the spray coating is worth it's salt, then it would be a good idea.

I have, in the past wrapped up my headers. But the wrap would retain water. Even after several hot days and runs, you could see/smell the steam. This and the thin metal of the tubes on some headers take a serious beating.
My headers cracked from the intense heat. The wrap company blamed it on me and not knowing how to jet a carb. Lean/rich conditions with a poor intake, etc..... a million excuses.

The theroy is sound. Keep the heat in the tube so the gas's stay hot. If the exhaust gas is hot, it will exit much more quickly.
If the exhaust gas cools, it slows, it bunchs up. The escaped heat, the engine sucks it in lowering power further.
(And then people wonder why a smaller tube exhuast pipe is used sometimes!)

OH, I went the coated header route. Thumbs up!