i run the invidia Gemini on mine, and i'm very happy with it. stock cats
it doesn't drone at motorway speed, and doesn't annoy my neighbours when i start up first thing.
and if you drive like a granny its not to obtrusive....however when you hit the loud pedal, and the revs build overs 2.5K then it really comes alive, and the sound is epic (especially through tunnels with the roof down, mine is a roadster)
also had it on the car just over a year, and had it up on ramps last week, and it still looks like it did the day it was put on...so very happy with the build quality and fit