On the few articles I lightly browsed I don't see the wind speeds this was achieved under. I mean, if there's an even better blow, could there be a even better incremental speed boost, right? I hope
Or are there design limits involved... a few more knots but not logarithmically so obviously...rhetorical question and curiosity mainly on my part.
The wind speed in which they set the most recent record (65+ kts) was in the high 20's (28 - 29 kts).
The relationship between wind velocity and speed is not linear. Drag increases roughly as the square of velocity.
What's more limiting to Sail Rocket is the shape of the foils - both the wing and the hydrofoil. Foils that work well at lower speeds don't work well at higher speeds. (This is why planes have leading edge slats and flaps.)
Additionally, the SR2 team has had problems with ventilation and cavitation on the hydrofoil. The addition of a fence allowed them to achieve a higher speed without sucking air down from the surface.
The hydrofoil also has a foil section meant to deal with cavitation (it's wedge-shaped, with a sharp leading edge instead of teardrop-shaped)