If you think the speed limits are there for your benefit as a driver, then you're looking at them from the wrong viewpoint.
Unless you're in something particularly cumbersome or challenging to drive, the speed limits will have no correlation with your vehicle's ability to move along without falling off the road.
Even the yellow signs that are there to help you with this at certain bends are merely "the recommended maximum speed in good driving conditions for the average car," according to the NSW RMS. So while these yellow signs do help you stay on the road, the key term for them is recommendation.
When it comes down to it, very few road rules are there to save you from yourself. Even those that do save you from yourself, such as blood alcohol limits, are still more about saving others from you. But the speed limits in particular are not nearly as much about you, the driver, as they are about all of the other people, with varing levels of mobility, with whom you need to share the road.
Such limits are there so that other people who need to do something as ordinary as cross the road can do so without the unwarranted surprise of you suddenly appearing at the exact same point in time and space.
As an example, I used to go for walks through Newington on my lunch breaks and there was one pedestrian crossing in particular not far from the shops where you had no chance of seeing a car heading up the hill at more than the 40km/h limit posted in that area. I'm sure you can think of at least one similar example near you. Probably several.
The same principle applies to anyone using an intersection. If the traffic being crossed or entered is going too swiftly, then big distance gaps still are not enough for this to occur safely.
I can think of one example in Faulconbridge, NSW where my sister used to live. People in the two lanes heading down the hill get impatient and speed up to 80km/h well before the sign allows it, but the bend, gentle as it is, still prevents traffic waiting to cross from seeing very far. Adding to the problem, people heading up the hill don't slow down to 60km/h before the sign. So, anyone turning right is faced with the challenge of diving across two lanes of traffic from a standing start and then (because the dividing island prevents any other angle) making a 90 degree turn into the fast lane, with all traffic usually moving at a velocity greater than they are supposed to. And if it's wet, forget it. Take a long windy detour around the back of town and queue up at the lights near the school instead. That's assuming you're local and know to avoid that intersection.
Again, you can probably think of one or more similar examples near you. And if you can't, try paying attention to all of the side roads you pass, and the speed at which the traffic is actually supposed to pass them.
You also need to share the road with much slower vehicles, and having vast differences in velocity even in the same direction makes things dangerous. How do they change lanes safely if you're barrelling along at a much greater pace for instance? And if you're travelling above the limit, you definitely have no right to be indignant about it when someone doing the limit does want to move across.
The weather is unpredictable too. Anyone who watches circuit racing will tell you it can be dry at one part of a track and very wet at another. It's no different on the street, where it can still be dry in one spot and suddenly slippery and wet in the next.
By this point into reading you may have also thought of stopping distances, and you're right, that is a factor. Whether it's for traffic lights, crossings, intersections, crests, likely traffic queues, driveways, or anything else, the whole point of speed limits is to give everyone the time needed to share the road and avoid having a collision.
So, as you travel around these holidays, remember the fact that there are going to be substantially more people than usual trying to share the road with you. Plus, many also won't be familiar with those roads either, including the common areas to induce anarchy that locals know to anticipate or avoid.
Sam Hollier is an ACM journalist and a motoring fanatic who builds cars in his shed in his spare time.