After doing extensive dyno testing on round track race engines, (at least 300 dyno runs) I pretty much got over the "headers breathe better" myth. Unless you're willing to custom-build a set of equal-length header tubes and adjust the length for a specific torque gain in a particular RPM range, the only purpose for a header is eye candy. They dramatically increase underhood temperature, and when, not if they start leaking, they destroy spark plug wires. I also got over believing in Santa Claus, the Easter Bunny, and honest politicians!
Jerry