if you do what hype8912 says, I doubt that the stepping of the header would be beneficial, but I am not familiar with the physics invovled so far as the 4-1, 4-2-1 design and why they do what they do per se.....however, if you were to do that, it would quite probably sound terrible (think weedeater), far from rumbly, however performance may or may not be better, I'm not really sure, I'd just y-pipe it myself.