At my first session - i tried my often used and old Speed3-21 and could not do more than 3 meters in very marginal wind because of my cangaroo-ing. After one hour - i was done! I slept well that evening!
Then i only used the 15m2 Speed3 because i realized its enough. There is never a steady wind here, the 15 stays even long in the Air as the 21 and if there comes a gust, its much easier to handle and much quicker at the edge of the wind-window.
A few days ago i got the Speed4-21 which i had orderd end of january and this thing seems to be much slower in marginal winds than the old one.
It could be possible to use such big kites with foils successfully in really steady wind-contitions - but not here in Salzburg on Wallersee.
One thing i noticed especially in foiling:
on higher speed - my kite doesnt like to go to the edge of the Wind-window and seems to stay in the more powerd zone. I have to grab the frontlines to depower much more than usually to get it to the edge and depower it more than normal.
In normal twintip-kiting - i edge more and the kite is forced to go to the edge. When i try this with the foil - it results in much more speed upwind but the kite looses no power.
Then - if its too much - the half foil comes out of the water resulting to the flat angle of the mast and acts more like a fin. A crash usually follows.
The only thing that works for me then is to bring up the kite much higher and steer the foil downwind to loose speed. But thats not working every time ...
But ill figure it out this summer i think.