speedo inaccuracy

I have been wondering about the accuracy of the speedo as well. I've done 3500km and the bike is loosening up nicely now. Other than the small shield and the resistor on the sensor to rich-up the low revs, mine is standard. We did a 360km breakfast run on Sunday and one of the guys has a rebuilt Honda CBX, it's a beaut, anyway he is always teasing me saying lets see what she can do, and don't stress we'll wait for you but I just laugh. So Sunday he pulls next to me, we are running at about 140km/h and gives me the eye then he whips open the CBX so i do the same. Well when the speedo reads 180 he starts to fade and I hang in till I see just over 190 then I shut it down because the cops are out in force on Sunday mornings just waiting for the bikes. At breakfast he concedes and says he tried but could not catch me, the Stryker is awsome. Yep the bike is amazing it sure has power and for the style of bike is pretty **** good through the turns as well and giving me over 19km/L, dragging the boards a bit too, but I'm still wondering what kind of real speed I did. Regards from sunny Durban RSA.