Yes, they run hotter, particularly when pushed. The good news is that a hot head isn't gonna make a properly built motor seize. You'll likely just get more pinging the occasional broken spark plug and maybe the exhaust valve clarances opening up resulting in kewl flames shooting out your pipes (ask me how I know). The way to avoid all of this is to keep the compression ratio at sane levels (7.5:1 tops) and making sure your timing is set right. IMHO, running too rich of a mixture doesn't help much but will build up carbon, making the detonation worse and putting carbon pits in your exhaust valve seats.
On the upside, I seriously doubt the header wrap does anything but make your pipes rust and crack, at least that's been my experience.