well unfortunately there isnt much info on replacing just the s-pipe b/c until now there hasnt been a replacement for just it...ions setup replaces the whole exhaust....my statements were based off of two things...the Ion sport exhaust was tested to net a 22whp gain(replaces s-pipe back), the CorkSport system netted 13whp and left the s-pipe stock, you can derive, though not exactly scientific, that the difference had to be from the restriction of the s-pipe. On a more scientific level I have the airflow rate around here based on the ID of the s-pipe and its fairly restrictive. If i remember correctly the ID was under 2"...its like a water hose valve the bigger the outlet the more volume that can flow through it. im willing to bet, especially at higher boost levels, that replacing the s-pipe will net fairly sizable gains in addition to the rest of the exhaust...but like you said I dont have solid proof this is just based on "off the cuff" calculations and experience with other turbo cars...