This boat is a pleasure to paddle in any conditions. It is very comfortable and well laid out. I also have a regular performance lay up V10. I would rate them about the same for stability, or maybe a slight advantage to the Mark 1. I time trialed the Mark against a V10 sport, and did better in the sport, and the sport is notably more stable (flat water test). So, obviously it would be that much slower than one of the front running skis (V10, Mako 6 etc). So why buy one? My understanding is that these skis are very popular for big water in South Africa. I think it must be due in part to the build. This boat and all its trim are much much more substantial then my V10 and a V10 sport I have used extensively.
I gave this boat a 9 only because it is a little slower without the benefit of increased stability. If you are not racing where every second counts, this is a great boat that will last many years.
I have paddled kayaks for over three years and started using a surfski just a year ago. This ski, although considered an "intermediate ski" can be mastered by a very motivated beginner. It took me about a month to be able to paddle a few miles or more without falling off. For surfskis, the boat is stable.
The speed of this boat is much greater than any sea kayak but some waterline is lost due to the extreme rocker of this boat. I have raced this boat and did well. In the hands of an able paddler, this boat can maintain 7-8 MPH with relatively good effort. I have sprinted this boat to 10MPH, GPS verified, but not for anything longer than a few hundred feet.
Stability: On flat water this boat is very stable. Also, it is a great downwind boat that surfs very well. The extreme rocker ensures you never burry the bow on large waves. The boat also performs well in sideways chop and swell. As many people have also stated, when going into the wind and large waves, 3 FT or larger, the bow does have a tendency to slap violently between wave sets due to the large volume and rocker in the bow. I would imagine this would not be a problem for a paddler over 200 lbs, but many others have found the same to be true.
Overall, the boat is great. I have been very pleased with its ease of use, stability, and speed. The boats construction and finish is very good.