no doubt majority of restriction is in the downpipes, they contain the first set of catalytic converters. switching DPs will give you the largest increase in power
switching midpipes is primarily for sound improvements, power increase is negligible. however i wouldn't underestimate the increase in driving pleasure from better sound though.
switching out downpipes will make your car NOT california smog legal, i'm not sure about midpipes, perhaps someone else can chime in
Last edited by dbchun; 11-16-2012 at 12:47 AM.