That's not entirely true, there are many spots on the autobahn where there is a speed limit (often for only like a mile, then you get another few miles of no speed limit, then speed limit again, over and over, it's really annoying). Though there are indeed some decently long stretches of no speed limits. Also, crashes that happen on the autobahn are pretty horrific from what I hear, luckily I didn't witness any. The BMW I drove in could comfortably go 140 km/h if memory serves me (it's been a few years), though rarely was able to get up to that speed since a lot of the autobahn is only 2 lanes and the flow of traffic wasn't particularly fast. When someone came flying up behind you going 40 km/h faster than you were you moved the heck out of the way; I'm not sure that's the best system for safe driving and I'm glad I didn't die.

QM

Look, I live in Michigan, and a lot of the people here think that speeding isnt a huge deal. They scoff when people berate them for speeding. And ya know what? We have the more driving fatalities than any other state in the U.S. That saya something.

10 mph is going to make a huge difference.

An increase of velocity of 10 mph is going to be an increase of kinetic energy of 26.5 Joules. Kinetic energy is proportional to the square of the velocity, so if you triple your speed, you have nine times the energy. That's nine times the amount of damage you do to the child you hit.

What's probably more relevant is going to be stopping distance.
Taking the coefficient of friction between tires and road to be 0.7, which is a fairly conservative estimate of good conditions and good tyres, the stopping distance (the distance you skid when you brake) of a car going at 30 mph is 15 metres.
The stopping distance of a car going at 40 mph is 28 metres.
That's not even taking into account 'thinking distance' (the distance you drive during your reaction time), which would too of course increase stopping distance. (Let's say reaction time is 0.2 seconds, if you're going faster you'll travel further in those 0.2 seconds).

You might 'understand' your car and your abilities, but you don't understand and appreciate the physics of motion. Speed limits are there for a reason. If individual speed limits seem inappropriate, then apply to your local council or whatever to have them re-evaluated, but the chances are that there's probably something in the area that you're not aware of. Speed limits around schools are much lower than other places.

Uber conservative:

I'd put the coefficient of friction lower, and if you're talking about skidding you've got major lowering again - like to point 2 or point 3.

Long long way.

Aside, I speed on the motorways - in Britain nobody really drives at 70mph, you have HGV's in the inside lane doing about 65, the outside laners will be cruising at about 80 or 85.

But anywhere else is strictly to the limit for me, I'm mainly driving around subburban areas with lots of kids.