My stock piped '06 YZ250 passes w/o a problem. The packing seems to be good for 3 events before the sound starts creeping up and it's time to repack.
re: loudness
What you hear vs. what the meter reads are not directly related. While some thumpers may seem loud, the meter may indicate otherwise. And the sound check is performed at half of the maximum operating RPM, not WFO.