Peter is right in a sense that the hydrofoil principle has no limited speed in itself ; so we could believe that by infinitelly reducing the thrust, your leg power and the cavitation, or whatever you want, we could reach infinite speeds ; same for the kite, it is not theoretically limited in terms of pure speed if its structure allows enormous loading and if the wind is high enough.
BUT ! there is a physical limit actually. It is linked to the Lift/Drag ratio of the kite. If you do the calcs and complete projection of forces, you will see that the rider speed will never overpass the multiplication [L/D ratio * real wind speed]. So here is a definite top speed limit, that will never ever be reached whatever improvement you do on the foil. For illustrating example, a standard race kite (assuming L/D=10) in 30 knots will allows up to 300 knots speed


