Wouter, some corrections to the speed of an A-cat with spi.
* In higher winds I sail 150 deg of the wind not 140 deg.
* The movie stated 6-12 knots and if you watch the waves around the boat it was white caps at the downwind in the beginning and later in the movie the seas was calmer.
* If the wind was close to 12 knots in the beginning the 18 knots of downwind speed is ok according to the 150% rule you stated.

/håkan