Kunz,
I've been on the road a lot. I didn't realize Pete had another header out there with larger tubing. I have the original header and stage II chip, so my results are with the original header. Can't help you with a larger version. However, like Bob said the laws of fluid dynamics apply and the torque curve would shift a bit to the right and should result in an increase in flow at higher rpms. Good for the track, not so much for the street.
I'm going to have my car tuned for next season by one of the local guys (Behe) to extract the power it should be producing. I had the head cleaned up, and it needs retuned to get the fueling and timing to match. Again, consequences from messing with the port sizes Porsche designed. I'm hoping I don't need to change the cams...
Joel