I'm running Langdon headers to a 2.5" exhaust, Y-pipe about 2' back, into a single 2.5" pipe, through a 2.5" Flowmaster 10 series, and out the back. I have a LOT more power than stock now and it sounds darn good.
The only way to tell if there's a difference would be for me to change it to a dual exhaust (which I might eventually do) and compare it with hard numbers. My gut is telling me there won't be a darn bit of difference because any minor gains I'd see would be lost with the additional weight.
