Bear with me, I haven't had a play to work the quote jigger on here, but I refer to the reply a couple of posts back to my paper tiger/arrow post.
I think you missed my point, Wouter. The original idea, I thought, but correct me if I'm wrong, because I am more often than not, was to introduce or design a 12ft cat, 13ft is around the 3.95m mark, etc..
I don't think changing the length of the boat is the answer, if it doesn't suit your design, or the parameters you set for yourself earlier, such as sail area, etc..
If I were to design a boat, then found it optimal at 4m would I be able to call it an f12?
I'm not trying to be critical, but goal posts seem to be moving.
And I have seen a young woman, I would estimate to be 50-60 kg, sail an Arafura Cadet competitively (i.e national level) and the boat had no problem with her being on the wire, and boss's son and a friend who owned the same Impara at different times, were on the wire as much as any other class.
Regards