yup its a waste, and hurts performance but does sound good since its so much deeper.
there are 600-700hp trucks out there still running 4" exhaust so don't tell me its needed for high HP.
From what I have been told, it can hurt performance because what happens is when you open that pipe up to 5" (or some nuts even go to 6") you give the exhaust gasses alot more room to expand once they leave the turbo. this has a cooling affect on the gas (think science: when pressure drops so does temperature) and this in turn slows down the whole exhaust stream, and the whole object is to get that exhaust out as fast as possible right?