42DD downpipe fitted on my S3....

[Jungleboi]

if your worried about the neighbors you could consider a varex exhaust on the end
i had one on my skyline, its remote controlled butterfly valve,
they have a cannon and a twin tip model
looks nice but can keep the decibels down

[SamS3]

I just got a Milltek non res fitted and it's not much louder than stock (with standard cats/downpipe) so I reckon a resonated one would be OEM like sound wise but with better flow? They are very well made and Dave @ ATPG does awesome deals on them.