> My guess is that automated driving systems will have to err on the side of caution and that this will result in seemingly (to the passenger) unnecessary slow-downs.

How are you expecting to be able to regulate implementation specific details like this across the industry? How would you enforce entirely requirements like this? If it's left to invisible hand of the market I would assume that the demand would be higher for cars with more aggressive driving styles, that will get you from A to B faster.