I am running a 3" cat-less downpipe into the stock catback on APR Stage 2. The power increase was noticeable, even before flashing the APR map. The sound is still pretty quiet at idle and cruising, but when you give it some throttle it's louder than stock. The exhaust sound is also more noticeable on cold starts until the engine warms up. Also the sound of the turbo spooling is much more prominent (which I like!)