Most of you are wrong here...
Of course there is a "practical" speed for a given hydrofoil that is difficult to go beyond, yes, and this is why smaller and less lifting wings will be able to go faster.
But no, there is no speed limit for a given foil (if we look away from the cavitation issues at higher speeds).
It is not drag that is the limiting factor for speed, nor the kites max speed (such a thing does not exist either, just as a hydrofoil can not have a max speed) - it is the kite power that limits !
How to explain ?
Easy - take a given huge draggy foil, pull it after a big superpowered speedboat, and now you will be able to get the foil to crazy high speeds, using sheer power
The same with a kite - even draggy low performing kites can go unlimited fast, when it blows sufficiently and you ride on a downwind course.
We have actually seen this quite often when talking speed records - crazy high winds and a normal low aspect kite, has been used for many of these - riding a deep downwind course.
As said, there is a practical limit where it feels like you can not go any faster, but this is solely because you have relatively limited power available when kitesurfing.
So it might seem like a given wing and foil setup has a max speed - and this is how it feels in real life out there because the drag is squared with your riding speed so the draggy ones will feel like anchors quite fast, and because of control issues it will also be harder to ride.
But it is not so, there is no max speed...
The draggy foils demands a lot more power to get to the same speed, but they CAN obtain the same speed as low drag foils, if sufficient power.
This is the reason why really good riders like Gunnar, can obtain a lot higher speed when riding say the Takuma wing, than most other riders who cant.
It is individual and depends on how much force you can get from the kite, thus it depends hugely on skill and wind strength.