I think there are many variables involved. My main commuting route is a 10 mile, 45MPH 6 lane stretch of road. I don't feel you put yourself at danger riding that slow as speed is not really a factor whether it is 45 or 35 MPH, you are still considered a slower vehicle. If I ever feel I am holding up traffic, it is as simple as pulling over into a gas station and waiting for the light cycle. Places are definitely going to vary. He is wrong in asserting that a shoulder is for parking and you should ride there. Where I am at, you are only required to ride in a designated bicycle lane. Non-designated zones are shoulders, and thus, not considered part of the road way. He disregards your importance by stating "You are slowing other people down." You are trying to get from point A to point B as timely and legally as everyone else. Really, it is up to you in gauging what you feel is your safest route to get from one place to another. In my opinion, he was wrong for pulling you over (except for the lights, which is required to have by law), but it is clear that he was pulling you over "for slowing down everyone else."