i actually use a 40 cm fin with my 7-oh
as a heavyweight, i really like this combination
so, ideally, even for myself , i would choose under 40 cm fin for 6.5 in an ideal world, butt since i have the 40, i would use that
since you are 40 kg lighter than me, i imagine under 40 cm would be great also
perhaps 38 cm fin, if there is such a thing ??
i find a bigger fin with a small sail is okay until the wind picks up
then the board gets too much lift and creates issues of "control"
people do not seem to pay enough attention to the board, sail AND fin combination
some speed sailors have dozens of fins - to get just the right feel for the combination and for the day's conditions
: is there a "significant" difference between 38 and 42 cm for a lightweight like the "lady" here ??