Dan,

 

Even though I am merely flying a lowly 320, I did employ the E.A.R. suggested noise supression material along with ensuring that the D-section (forward of the main spar in the stub wing) damped the "guitar sound-box" effect.  I have various foam/dead aluminum on the firewall, nose wheel well, bottom and side fuselage walls as far back as the seat back.  Unfortunately (for me), after attenuating those noise sources, the cabin cooling NACAs and the "hot-house" canopy (3/16", Later versions were thicker) contribute more to the cockpit noise (prop generated) than those supressed areas. 

 

I would think that all high speed aircraft would benefit from even thicker canopy "glass", wee props (if any) and a more indirect cockpit cooling air source. Or, maybe we should just all wear HELMETS with ANR (ignoring any passenger needs - see ***).