Mat, I think for those of us who use buses we do have a right to comment as we are in these buses all the time.
They probably have very tight schedules but those drivers who drive unnecessarily fast in non-rush are 'bus captains gone crazy' and this is wrong. It happens far too frequently and I don't believe later at night this has anything to do with a tight schedule, just how they want to drive.
They also rest in many terminals too for those who have never seen a terminal. It is not an easy job but it seems to me for HK it is a good job. I am sure on some routes they feel pressure if they are on timed runs and being timed. I won't take the 691 bus from Macau Ferry to Kwun Tong in rush hour (go MTR as it is cheaper with the fare saver) because he can't get out of Central for what seems far too long and then from Tin Hau to North Point it is like a fast ride in a square wheeled chariot as it looks like the bus captain is trying to make up time. I want to read the paper but can't as I am hanging on and bouncing around. There are many other very smooth bus rides on highways and I take those too. 720 to and from Shau Kei Wan is usually just fine when I take it.
There is no excuse for turning one of these buses over if you drive at a speed safe for the road and the road conditions unless maybe the vehicle is defective. To avoid being negligent you must drive at a speed that anticipates unforeseen problems like oil slicks, pot holes or stopped vehicles where they shouldn't be.
In vehicle speeds the 85th percentile rule used by engineers basically says that 85% of the drivers will find the correct speed for the road and conditions and that they don't need a posted speed limit to find it. It is the other 15% like a speeding bus captain you worry about.