I don't know about backpressure on my SuperSprint exhaust, but it sounds pretty damned good and throaty without being over the top. It definitely growls more than the stock exhaust, and it doesn't drone at speed either.
1962 Porsche 356 Coupe Champagne/Black
1988 Porsche 911 M491 Cab Granite Green/Linen
2002 BMW M3 Coupe Carbon Black/Black
1992 Porsche 968 Coupe Black/Black
1997 Porsche 993 Coupe Arctic Silver/Black
2001 Porsche 996 Coupe Black/Black