I agree with everything Z just told ya, Karl. And if as Rich just noted here, you've mostly worn a half-helmet in the past, then going to a full-face model will seem strange to ya.
And thus, this is why I feel your best bet for that long-distance ride you have coming up out this way, and one which during that long ride which I know from past experience occasionally having the option of covering your face with a shield is far less tiring on a rider than any open face in either 1/2 or 3/4 style will provide you(especially on those Interstates), is precisely why I endorse Z's thoughts about a flip-up or "modular" helmet.
And, while I have yet to try this one out, the Shark helmet that Z mentioned and which allows the option of an open-faced or as a full-face, and which the chin-bar folds completely back and out-of-the-way and thus would still be aerodynamic when you're using it as an open-face is this one...
http://www.revzilla.com/motorcycle/shark-evoline-2-st-helmet And, at the price they're selling this model at this website, it sounds like a great bargain to me.
