Don't need conversions, we still use Imperial measurements (ie. miles) for our roads. Yet we can be criminally prosecuted for selling food items in Imperial measurements.
So the highest speed you get is 65 mph?
We have 5 mph, 10 mph (both normally on private property that many people use, eg. caravan sites), 20 mph (used in areas where there are a
lot of kiddies on the streets running around), 30 mph (standard inner-city speed), 40 mph(standard for roads tht run through residential areas with drives, ie. slightly less urban areas), 50 mph (not used much, but is seen sometimes), 60 mph (normal speed for anything without another speed, most B (country) roads), and 70 mph for motorways and dual-carriageways (which are either 2, 3 or 4 lanes each way).