Agreed the test is not perfect, but it gives enough controls to make a decent comparison between systems. You could always test under different conditions and post those results also. For example I drove around with the max metering on and the loudest "in cabin" level I got after about 15 minutes of doing some WOT runs was 105 db.
The 2/3 of rpm at a distance of one meter is just a set of controls. Its not perfect but it should give members a little bit of clarity on a subject that is rather speculative around here.
I would say to feel free to post other results under other conditions, we could even have a decibel contest so to say. loudest exhaust gets one of these --->
, sorry I'm cheap....