Although satirical...
You don't need a sound meter... motorcycle manufacturers generally push noise right right up to the legal limit when they certify bikes. If you are making it louder, you know it is not legal.
As to your last point, you dont need a loud bike to have performance. I doubt anyone can take, for example, a Ducati Streetfighter V4S any where near where more performance is needed on the street. Of course I would be REALLY impressed if you can stay within the legal limits of street riding and actually NEED more than 208hp on 392lb bike....