When fast scrolling the tacc speed scroll wheel it works in increments of 5. In km/h countries this should be adjustable to 10 increments which makes much more sense since the speed limits work in 10 increments as well.
In the UK the road network uses miles and speed in miles per hour which are mandatory. However, many people use metric measurements for short distances like centimetres and metres in their daily lives so don't use inches and yards as these are not mandatory to know.
In navigation, rather than just negatively framed warnings about needing to be at a certain speed to reach the destination, provide "smart suggestions" regarding distance gained/charge retained if speed was reduced.