I think they say Jap bikes are notorious for the speedos to be about 5 to 7 percent off.
now, when you do land speed racing you learn that your tires are slipping a lot when you are at these speeds because of traction loss due to a lot of reasons and that speedos are accurate at around 60 mph. so give him a 10% correction factor and all is good.
But it is amazing that you have a place to do that legally. I would piss in my pants to find a road like that here.
Killer video