Futura 122 Fins

[Windnc]

Yesterday I sailed my Futura 122 for the first time. To start I weigh 90kg (200 lbs.). I started out in 14-15 Knot flat water conditions with an 8.3 cammed race sail. I used a Maui Fin Co. RC2 46cm fin which worked great with this sail.
Later the wind increased to 16-18 with gusts -20K, so I switched to a 7.3 cammed race sail and put the Drake 40cm fin on that comes with the board.
I mounted the mast base at the recommended position on the board. By this time the water was getting rougher with 1.5 -2' chop wind swells. I noticed that the fin was spinning out frequently, especially when I was pushing the board hard upwind, and getting it to re-engage without slowing down considerably.
Later I rigged a 6.8 Freeride sail (no cams), same wind speed, and still had spin out problems with the Drake 40cm fin. I was trying not to push too hard on the fin and I am a very experienced windsurfer, including Formula sailing, but am new to this type of slalom board.
So I am wondering if others have had spin out problems with the Drake 40? Should I get a better race or slalom fin in the 40 cm range? Perhaps a 36 cm?
Any thoughts/recommendations are appreciated.

BTW, I love the board and it rides and jibes beautifully.

Chuck