Hi Craig,
Is there one of those signs that gives your speed near you?
I drive by one of those when I am trying to check my speedometer accuracy.
On my Virago 250, the sign read 28 mph when my speedo said 30 mph.
Then I got a new front tire - now the signs says 29 mph when my speedo says 30 mph.
This way you will know how fast you are really going.
You can mark your speedo if you want with the correct speed - if 120 kph is really 100, then put a small sticker saying "100" over the 120