There are lots of conversations about what you cant do on 12'6 race boards and how they don't perform well on downwinders in the last few weeks.
Size and weight of the rider is obviously a factor but Kristi Page, Simondo Baum and Justin Ormonde have done several runs in extreme condition and had nothing but fun and the 12'6s do work in 35-45-50kn
This is a vid I posted a while back, vision is not great due to wind squalls and in a homer moment i forgot the tripod but you'll get the idea.