I have the turbo back Stainless Steel 3" CES exhaust system on my R34 Sedan which comprises of a Split front HPC coated dump, hiflow cat, smaller muffler and a Magnaflow Muffler (3" in to a twin 3" out) and it is very quiet. It passed the wife and new born baby test easily.
At the last Skid Pan Day, people commented on how good it sounded from the outside with a nice deep tone, but without the droney sounds inside the cabin.
And since then people on the street have also commented. I couldn't be happier with a 87dba and fairly free flowing system.
My 2cents