A long time ago the late Jere Stahl told me that headers were a 5% deal. That is from the best to the worse you are talking about 5% of your power.
I don't know how much the difference between a header that is good compared to a header that is great, but you probably are not going to help or hurt things a whole lot.
And then there is the "Engine Masters" episode where they beat the daylights out of a set of headers and have little effect.
