yeah your right its all the combo....Paul's car is really a testiment to that(of course being a sick driver helps as well) in an NA app the chambered muffs may make a tad more power because i believe they are a little more restrivtive, hence giving a little more back pressure and creating more torque....but on a boosted application you want that exhaust to get the hell out of there so you want a more straight through design....with that being said i doubt you would notice the difference in a catback on the SOTP dyno OR at the track...maybe a tenth, tenth and ahalf most....
Anthony