As many others mentioned, the speed ain't the reason why C-D is always chaotic. It's the drivers. Even if you lower the speed limit, trolls will still troll around and bad apples will still be bad apples. On top of all that, think about this. Currently, the speed limit systems are like this. City: 60km/h (unless speed limit is higher than 60), and everywhere else is 110km/h. Even in cities, if the speed limits are different, the max speed you can go is different. Now back to C-D. Like people have mentioned, there is a part of C-D where the speed limit is 80km/h. This is mostly due to the (70%) straight roads at that part. If we were to make that part 60km/h as well, wouldn't it be pointless? Even SCS thought about this when making the speed limit and adjusted it accordingly, but if we were to just ignore that and make it 60, isn't THAT a waste of time? I see you have also mentioned about the more lanes, less traffic, uhh about that, just search 'Katy Freeway traffic' on Google. Lastly, I just want to say that even TruckersMP acknowledges about speeding and while not recommending it, actually allows it.
§2 - Game only rules
(omitted) Speeding, while allowed, is not recommended. Speeding can lead to accidents and can factor in a punishment decision. (rest is omitted)
i hope u understand sleepy me typing english, gud night