I agree with many points made here. Personally, I don't think that my appreciation of speed in relation to road type had been significantly tested until I moved to (very) rural Dorset. Since then I have learnt the following:
1. As Jake says, a significant number of drivers drive at 40mph, no matter where they are, what the speed limit is or how dangerous that might be.
2. After stopping to check if 2 drivers are OK following a very near miss just ahead on a blind bend with enough room for 1 and 7/8ths of a car (the typical road width around here), your mouth will drop open when the driver who was clearly going too fast for the road condition, who's car is half way in a hedge, states that 'well if it says 30, you must be able to go at that speed'.
3. You can go at 30mph around a very tight country bend on a narrow country road and you might be OK.
4. However, if you meet a tractor, a driver from number 2, a lorry, a horse, a sheep, yet another loose farm dog, a deer, a cyclist or a teenage skateboarder who has decided to have some fun on a hilly road with bends, you will end up in a ditch, in a hedge, with no windmirrors, calling the RAC or, if you're very unlucky, take out the side of someone's 15th century thatched cottage.
5. Number 4 meetings happens at least 4 times a week and emergency stops, even when going very slowly, at least once a month. You HAVE to appreciate this or risk lives.
6. Rural roads may look like they take 2 cars, until you meet another car and realise that in order to avoid them, you will need to 'fall off' the side of the road and hit the rutted, pothole come small ditch at the side which WILL break your wheels, puncture your tyres and make you change your car regularly in the hope that a 4x4 will do a little better.
7. Tractors go by rule number 1, especially when driven by one of the farmer's sons.
8. You would be better off hitting a wall than a tractor because the tractor might just go straight over you instead!
I have experienced or witnessed several of these events and I will never again look at speed limits in the same way. To say that they are 'hopeful' around here is an understatement!