Header power gains

[RipShift]

ok I did the search thing and found all kinds of threads on headers, but most of what they talk about in there is just which header is better quality or which one is more cost effective yadda yadda. I want to know how much power there is to be gained from a header of one brand or another. Or are they really just so close that the choice really is just about the quality of the workmanship? Thanks guys