I liked the extra top end power on my recently purchased SW 3" Cat-back, but lets not even try to be diplomatic- it's pretty much loud enough to piss off your neighbors and give you a headache on a long trip.
So I got some C6-Z06 mufflers with the NPP exhaust flapper valves (vacuum actuated).

Note that the inside pipes are the loud, high flow straight thru section. This will be blocked during cruise conditions.
Hacked them off to put them on my loud-*** SW mufflers.
Working out the fit- had to rotate them a touch to fit the vacuum can.
Also the diaphragm comes loose and you can reposition it so the vacuum nipple points in any direction.