I am not Toby (although the post is from Toby he didn't write it...) but here go my two cents: i have the 8m and 10m Nemesis. At 83kg i think that i won't need the 8m. I have ridden the 10m with 27m lines in 32knot gusts without even feeling close to overpower. The 8m would be good for 35-40knots and in those conditions i am planning to stay at the beach. But i am waiting for them to give it a go
In 20-25 knots i go upwind and surf with the 8m but i like the 10m better.
The 8m is good for maybe a 70kg rider.
I hope this helps!