All has been said by Ken and mcross.
I use a 64 fin with a lot of flex in the tip (Deboichet R12) with a 10.9 sail and the standard 58 fin with my 8.8 sail.
I would like to add that In the real low wind range, i.e. 8-12 knots, I sometimes have a hard time to push it upwind. This is where my F161 used to excel. It's about the only minus I can think of if I compare the US147 with my former F161.
IS87 / IS101 / RRD114 / US147