There was also a post about this on the CB500X Forum a couple of years ago. It was found the American speedometers were accurate in MPH, but the Canadian speedometers in KPH were optimistically out by 6%.
The flashing road side KPH signs show that my CB1100 EX is also optimistically fast. I already knew that from riding on divided 4-lane highways. Ordinarily most people will drive their cars 10 to 15 KPH faster than the 100 KPH speed limit. But I have to ride about 120 KPH to keep up.
On 2 lane highways the speed limit is 80 KPH, but most people drive 90 KPH. I have to ride at 95 KPH to avoid being tailgated.
Canada's 2 lane highways use to have a speed limit of 60 MPH (100 KPH). But when Canada converted to the metric system, they were reduced to 80 KPH (55 MPH). Nobody noticed.
Now the price of gasoline fluctuates between $1.00 to $1.15 per liter, and Canadians accept that as normal. However if the metric system had not been used, gas would be $4.55 to $5.25 an Imperial gallon and people would be screaming.
Actually people do complain about paying $1.00 per liter for gas. A product that has to be drilled out of the earth as oil, piped to an American refinery, shipped back to Canada to holding tanks, and delivered by trucks to gas stations. But think nothing of paying $1.50 at a gas station for 1/2 liter bottle of water, something that is available from any tap.