Midnight, Do you think the Shoei would be better than the C3 for its supposed more chin room area for boom mic? Is there a slimmer or better setup than HD's boom? Long distance I use an N103 and had to carve a little foam out for boom to fit comfortably. Looking for another helmet when not using a cap and hand down my Nolan to BSR.
That would be a tough call...I'd read the Webbikeworld review on both helmets and see which one you may like best. Pay particular attention to what they say about head shape as it relates to both helmets. Those folks do an excellent job in helmet reviews. Take a look at the Nolan N104 review as well...from reports I've read, both here and elsewhere, it has more chin room than other Nolans from the past. It's also easier to ride with the chin bar raised on the Nolan, though you'll still look like a Nimrod. The Shark Evoline 2 is the only helmet I'm aware of that converts to a true 3/4 helmet when desired. It is a very nice feature, but the helmet is a bit heavier because of that feature.
The J&M microphone is considerably smaller in size than the HD. My wife has the J&M in her Nolan N102 and it works well for her. I used it in my N102 as well, but got a new helmet so made the HD Boom! that came with the bike fit. The Shark Evoline 2 ST has more room in front of the mouth than does many helmets.
The noise factor would probably push me towards the C3, all other things being equal. Both are excellent helmets though.