I was in the same boat as you (
) just a short while ago!
I have been paddling surfskis for 18 months and currently paddle a Robberg Express (updated version). My experience with the Robberg may not be exactly what you are looking for as it's my 3rd boat since I started but you might find my views helpful nonetheless. I started on a Knysna Kayaks Stingray but quickly changed to a Red7 Surf70. I never really felt comfortable in the Red7 as we do a lot of around the cans type racing in our area and the Surf70 tends to handle like a barge. At 21kg, the boat was also quite heavy and I never felt like I could get it up to speed unless I got it onto a big wave.
The reason I finally changed to a Robberg, was that it seemed to be a boat aimed at the lighter paddler. I'm 1.8m (6ft), 75kg so this seemed like a good fit for me. My boat weighs just under 15kg (Standard glass) and handles extremely well due to (I assume) the fact that it has more rocker built in. Of course, in theory this will affect the speed of the boat but I can say that I feel much faster on the boat due to the added acceleration off the mark. My top speed in all conditions has improved and although I'm still very much a back marker in the races, I have seen great improvements since getting in the Robberg. I've had to add quite a lot of padding in the cockpit but I like a good, snug fit. The guy I bought it from was selling due to the fact that the cockpit was too snug for him and I would peg him at about 90 - 95kg so I'd say definitely paddle it before you buy. He said he was fine for the first hour but then the pinch would get to him so a good, long test paddle is a must.
I bought the Robberg with exactly the same idea in mind. I'm in it for the long haul with this boat. Every time I paddle, I appreciate how light the boat is, from getting it onto the roof to accelerating off the mark. Stability wise, who knows? Initially, the primary stability definitely felt less than the Red7 Surf70 but it's definitely less of an issue now. I have been paddling it for about 6 months so the time on the water has definitely helped. I have found the subject of stability to be a difficult one as every person's opinion is based on how they feel in the boat and that has nothing to do with how I feel in the boat. The reality is that surfskis feel unstable when you start and with time, they feel less stable.
To end off, I'd say that if I could do it all over again, I'd buy a Think Evo or Mako XT to start with and paddle it for at least 1 year or 18 months. The reality is, that after 3 months and even after 1 year you're still a novice in surfski paddling so don't be fooled into thinking you'll be bored of a 'starter boat' after 3 months. These boats cost a bit more on the second hand market but they also retain their value well. There is so much to get used to and experiment with when starting on a ski that it's a good investment in building your basic skills and confidence.When I started, I didn't know enough about the sport to make an educated decision but you know what they say about hindsight. I definitely think my progress would have been faster on a more stable boat in the beginning as I am only now, after 18 months able to work on the finer points of my technique without worrying about my balance. The Robberg is a great boat but I don't think it's the best starter boat.
Good luck!
Wayne