My Termignoni's give my 1262cc engine an additional 15% horsepower, creeping up around 200hp.
I'm a show off, I mostly cruise the highways and coastal/country roads doing the speed limit, at times (when safe) I open her up and pull away from the traffic at a set of lights, the loud exhaust note is awesome, music to the ears.
I never race past the elderly or females, I'm not a bully, I care for other road users and hate those noisy bikes that race past female riders, these girls scare easy.
In Australia my cars, mostly V8's had dual exhausts with extractors/headers, loved the sound.