I'd say it's giving me less than 2-3 feet, without slowing down. Or maybe I'd define it as "I feel the wind from the passing car more than I hear the noise."

I think many of the honkers may actually be well-intentioned. Sometimes people seem to do it because they expect you're an oblivious cyclist who doesn't know the rules of the road and is blaring music through headphones... there are a lot of those around here.

Though I agree about how annoying and startling it is.