In New England, topless season for me is ~late March to mid-November (thanks to heated seats).
Seeing where you live, I think you're going to experience a lot of road noise given the size of the highways and the resulting traffic levels. However, on a smaller quiet road and at lower revs (OK speed, just not revving highly) I'm perfectly able to hold a conversation in the car when "topless" at a normal volume and even on the highway without getting hoarse. If I remember correctly, there is a road out there that offers a nice twisty jaunt over to Half Moon Bay through the (Santa Cruz?) mountains that would be a nice quiet ride... maybe you can test it there and see for yourself.
