I have a Spec billet flywheel in my S3. the noise is acceptable when the AC is off. If AC is turned on, it rattles like a mofo...
The only thing is, that you have a lot more noise and vibration when you are breaking on the engine.
But in combination with a Sachs organic race clutch (I have the one without springs in it, zo no dampening at all) it drives awsome. launches @7000rpm go flawless. And you can drive normal.