In reality I would simplify it thus:
Standard exhaust - quiet but acceptable (just!)
Twin sports - permanent V8 rumble (ala TVR) quite loud to very loud all the time.
Side exits - Quiet at tickover barks like a spitfire. Loud as revs rise, imagine being overtaken by two Harley Davidsons.
BtG
I'd totally agree with Boshly's descriptions of the above systems, and with the std side pipe set up, it does sounded like Harley Davidson at motorway speed when you put your foot down
