This is a something id also like to hear about from members who have actually have tried or have one fitted!
From a performance point of view its the best way to go, but from a trackday point of view it would need to be less than 105db, I had my goose tested at 101 with the 5" tail pipe, Iv know got a full 3" system fitted and id guess its louder than the goose,
Once i get my car mapped, m.o.t'd and taxed a db test will be my first point of call