RE: From Adam in kernow
Way too large a fin for pure speed
You can use much smaller.
Speed sailing - the fin is crucial.
I use a Falcon 2005 90litre (60cm width) with a 26/28cm fin for downwind - Max GPS on this board 38.5 knots in Choppy/Flat water.
Simon Hinkley Recently used the 105 Isonic with 32/34 fins and was hitting peaks of 33/34 knots at choppy marazion with a 7m.