There are high 45mph speed limits where I live and most drivers blow that by 10 to 20 mph all day everyday. While you want to keep an eye on your mirror, the real dangers lie in drivers turning (right hook or left hook) into your path, typically without signaling, especially when it seems like you should be in plain sight and there is now way they could turn at that moment.
IMO, the key is keeping a peripheral awareness of the front wheels of nearby cars or cars that have an opportunity to turn even if they haven't signaled. That is your split second warning to evade. I had two near misses in the past week or so that I appear to have gotten through due to that slight edge.
There is nothing you can do about drivers buzzing your elbow over the speed limit, except maybe taking more of the lane (doesn't seem to work here). For that just focus on enjoying your ride, your cadence, etc.
Last edited by Chesha Neko; 12-18-12 at 03:45 PM.