It's percentage scaling, so a percent increase of a small number isn't that much of an increase. Your examples of 50, 55, and 60 miles per hour seem like incredibly low speed limits for highway travel, from a United States Perspective. So for plotting distance routes, we would very rarely have numbers that low. So sure, 125% of that would be more reasonable. But a lot of the states in the western U.S. have 75 or 80 mile per hour speed limits, and I've seen people throw out that idea of using a 125% ratio, which yields 100 miles per hour (161 km per hour) and then they are shocked why the driving range estimate looks so short. So with highway speeds here, 1.1 ratio is a bit more normal for typical speeding behavior at higher speed limit highways.
And about the 70 speeding to 90 miles per hour? That is going pretty risky. Some people do it, but it is very likely to get an expensive ticket. There is a saying around people who know police officers that some officers even use themselves about their decision thresholds for levels of speeding:
"8, you're fine. 9, you're mine." So if you're about 9-10 miles per hour over the limit in a lot of places, that really increases the chances of getting ticketed.
... and maybe decouple it from the default cruise speed too while they are at it.
