Sorry, I have to disagree: I once saw a police reconstruction of an accident in which a kid was run over on a suburban road by a car doing 60mph. They filmed from inside a police car as it went past the spot (over the crest of a hill) at 30, then 40, then 50 then 60 mph. At 60 there would have been less than 2 secs to see the kid crossing the road, react and stop. That is definitely NOT a lot of time (unless of course you're Superman...)The car went past in no time. THAT was scary, and made me think.
As a biker you also have to take into account that people do not EXPECT to have a bike coming towards them at the speed of sound on a quiet road, so anything more than 20mph over the limit increases the risk that they will pull out on you.
On top of that it is important to realise that once a car has started moving, the driver will be looking where he is going, and if that is not towards you, he WILL NOT SEE YOU.
Finally, when trying to avoid someone, try to go for the overtaking manoeuvre, as their most instinctive reaction, once they realise you're there, will be to dive for the verge.
When I got this wrong (doing 50mph in a 60 mph speed limit) I came across a car in the middle of pulling out of a driveway round an inoccuous (sp?) bend, and went for the disappearing gap between the car and the verge, leaning on my horn and the brakes. Ended up at the same speed as the car, alongside the car, but on the verge. Got caught up in the hedge, bike went down and broke my leg.
If I'd been on a sportsbike, I could have stopped (it was a trail bike). If I'd been going 5 mph slower, I would have ended up behind the car, at the same speed (what's 5 mph? Would you know?). If I'd gone for the overtake, I'd have ridden past shaking my head. And if my aunt had balls....