I would argue that it wasnt reasonable even when turns were 6 times too long. CDDA strives for reality, but there are some limitations, and some things like for example weapons firing range need to be be scaled down only to feel good, not to be numerically-correct with irl data. When turns were 6s long everything involving fighting and moving was already scaled to feel like 1s. But not vehicle breaking. You were able to stop a truck going 120km/h in 12 secs, and there were people defending it. During theese 12s (2 turns) the truck covered distance of about half its lenght.
IMHO best solution wouldnt be really inserting exact IRL data, bacause distance is relative (5 tile long ambulance isnt 5 meters, 3,6km/h wont give you 1tile/turn etc.)
Insted make it something more like this:
-you go through crowded city full of wrecks at 120 km/h? well, you die
-you go through a city carefully at 40 km/h? Then in reward you will be able to react when you realise there is something behind a corner.
-you go at middle speed, lets say 80? well, you can try to brake, but you might loose controll, and braking distance should be like a few lenghts of your wehicle. You might still hit your freshly spoted obstacle, although at lower, non-lethal speed.