just bought a supersprint system from the cat back, £409 inc vat(dtm rear box). apparently the reason stainless isn't used on the outer of the rear box so much is because of booming noise, particularly on motorways(i believe the inner is actually stainless, as are the external pipes). thay also do a de-cat bolt on/off silencer for 106+vat. hope they're good! a local exhaust specialist has offered to make me up a de-cat pipe for £30-£40, wondered how much difference the de-cat makes?