Wouter, no miracles in here. The final result is calculated as a difference in corrected time (negative u win, positive I win). If you combine two results with errors in a sum or difference, the error of the result is calculated as the square root of the sum of squared errors of each variable. Thus err=Sqrt(70^2+70^2)=100. Of course, saying that 100 seconds is "almost" 2 minutes is a matter of taste.

However, the actual numbers are not important. Make the error 2.5% and you get 2 minutes (ok, 124 seconds). The important thing is that we are using very simple parametrized formulas, which might give an idea about the speed of the boat but which have an error (which depends on boat desgin, winds, waves, etc). In physics, I have never seen such simple formulas to describe reality within a 2% error over the entire range of variables. One should have in mind this "little problem" when reading results based on ratings.

Rolf, having in mind this, I don't think neither fast nor slow boats have an advantage. It's the combination of design (i.e. daggerboard yes/no spi yes/no modern sail plan yes/no hull shape, wind conditions) which fixes if you have a "good", "bad" o "correct" rating with your boat.