I ride the 7m and 9m, surfboard, 4line 190 lbs ,..
the 9m I can ride from 10mph if steady, up to 40mph when brutal gusts hit.
Comfortable riding 18-28.5
epic riding 25 steady.
having just a day in the water 10 - XXX
Best for around 20 mph.
I like it powered up.
Today was 10 to 30+ and I had a blast cause we had over head high waves.
Handles gusts real nice and de-powers great, but I fly it with a 2012 Naish bar. More throw I think, also bigger diameter bar, like it better. ( and got a kick as deal for it from da Tut )

I am 70kg and ride TT
the 9m works from 15 knots, moving it a bit in the air. high end for me is 25kn, 3 days ago I felt scared when it mounted above 25 with gust 30kn

the 12 from 11-12 knots, high end below 20kn, I don't like to be overpowered

hope this helps