[Nick Koan]

Headers don't necessarily increase diameter or reduce flow if the designers know what they are doing.

Headers, like all parts, can be engineered to give you what ever you want, and the GT Spec 2 headers are ones that help increase low end torque. Headers can be designed to give you more low end, more high end or more midrange. Cheap headers, or headers designed by people that don't understand all the variables (flow/heat/etc), will invariablly be awful for your car. But well designed ones can help you in a lot of ways.

To say that headers on a turbo car has more negatives then positives is pretty ignorant of the whole picture. Most headers that came out for the Subaru early on were poorly designed, so lots of people latched on to the idea that headers for Subarus are bad. They aren't bad, if designed properly.

Another caveat is that you will need a reflash to fully take advantage of well designed headers. I don't think Cobb AP has this functionality built in since they seem entrenched in this idea that headers reduce performance. Protuner will probably change that when it comes out.