Stock exhaust manifolds vs headers

Where do you want the power and what cam are you using? High compression and wild cam will benefit WAY more with headers than a 9:1 with a cam slightly larger than factory.
I want to have the peak power band around 3.5-4.5k rpm and 5.5-6k redline (Im used to alot more high revving engines than the SL6 so if this is too high I apologize). I'm not sure what cam specs to use, I plan to have a custom grind by a local cam specialist and all of that is still up in the air. Since my machinest hasn't yet determined how much overbore the block needs to just clean it up, I haven't yet run any compression calculations.