i have done removal of sound deadoning, back seat, rear seatbelts, parcel try trim, boot interior, spare wheel/jack, speedstar zero's (pretty light in comparison to other wheels i've carried)
overall i think the difference is more like adding a pod filter to a stock car.. make a tiny bit of difference.. but it seems like a whole heap cos it's really loud!
i think the bonnet makes a differance. ive got a carbon one and turn in on my car is alot nicer than my last one.
78's