Well, my dad and I use a hand held gps receiver and compared it to the speedometer in our car while driving. And as expected the speedometer showed a few knots faster than the gps, however the difference was not 73 knots and other crazy numbers as mentioned here on the forum. We therefore conclude the gps to be quite accurate (I know some will want to shoot me after writing this, but living in Oslo, Norway with an entire ocean to cross for most of the forum users, I'll take my chances:)).
Up hill we have done 13,7 knots in our Taipan 5.7 in around 12 knots of wind with zero waves. Down hill we have done around 20 knots, wind strength 15 to 18 knots. We did not fly the chute, so I reckon it is possible for a more experienced crew to go quite a bit faster while flying the kite. Opinions?
Regards Jimi