I'm from Finland where we have this kind of "relative fines". While I generally agree with the concept, it should better take into account the household's total income & wealth. E.g. I could get a fine of 1/2 of my monthly net income for driving 140 km/h (87 mph) on highway, which would hit hard our household (three kids, low income spouse, no savings), although no real harm or risk was caused to anyone.
That sounds pretty reasonable to me, frankly. That’s considerably over the limit, isn’t it?
The highway speed limit in a country like Romania is 130 kph, but you only risk getting fined if you exceed 140. As such, I usually do 130-135 kph on the highway in my small 1.4 l hatchback and I don’t feel unsafe at all. I feel much more unsafe on 2-lane national roads with lots of curbs and where you risk getting a horse-drawn carriage in front of you out of nowhere, even though on those roads people usually drive much slower (the limit is 90, I stick to 80-90 most of the times unless I have clear visibility for like one km, in which case I push it to 100). Point is that it’s not the speed that kills you, it’s NOT adapting the speed to the road’s conditions that does it. As such, imposing draconian speed limits on highways (like in Finland) is very counter-productive and frustrating, because those highways are actually built to “support” higher speeds (just look at Germany).