Headers are a toss-up - depending on how they're made. The longer they are, the more top end you'll gain (but lose on lower end). The shorter they are the more torque you'll gain on bottom end but then the top end suffers. (I have adjustable headers on my bird and that's for tuning at the track for temp, surface and other variables)
Personally, for a street driven car, I'd avoid them - they don't wear well for year round driving, they generate ALOT of heat, they're noisy, and finding ones to fit your driving (in all conditions) can be tough & costly.
First decide where you want your power band and consider all conditions (year round weather, the types of driving your planning on doing not just those blasts down the highway, and the "big-gees" - what you're willing to spend on mods & maintenance.) I'm an advocate for mods as long as you know what the repercussions are before learning at your wallets' expense.