I am looking at the Quicksilver exhaust. They have dyno tests of 6-8bhp for the cat back exhaust. They have a very good reputation and the thing i like is that it's not much louder, but creates a richer note (don't think the boyracer theme suits the mini).
They also do a downpipe and sports cat. Combined dyno figure of 18-20bhp! Altogether thats around £700 though.
How do dealers respond to people having non-
JCW exhausts?
-Rob