Not sure I agree with Stoff in not being able to drag back to your board.
When wind is strong and you put it to edge of window, then you can really get upwind dragging. Easy as, unlike when is low wind and you have to move the kite farther back in wind to gain power.
But I do agree best to be sensible.
I am 83k and my old 11m was good to about 28k but my new 10m is better by 3 or 4 knots as long as it is consistant. Not sure what is the range when the kite is getting hit in sudden gusts that are unpredictable.