pull the engine for headers?

Not trying to be a smartass, but how much hp do you really gain by headers? Is it really worth pulling the engine for?

on average, people say, it will give 20-50 more hp with mod headers. will you notice the increased hp? not if that is all you do... :P im planning on putting headers on, new pully sys, flow masters, p/p everything. along with my k&n

got me a module on order for my limiter, so with this here, if i dont see any noticable gain in power, then im selling this, and getting an SS :P bleh... i will put the blower on that, with the nitris, and new pullies and headers. that will fixor my problem... :P