Unless you are really powered up and interested only in top speed, my experience with Wolfgang's Duo Weed fins (I have the 28/32/36/and 40 cm) suggests that you might be happier with the 32 cm as it works in a wider variety of conditions with both larger 7.8 m2 and smaller 5.6 m2 rigs).
Also, since you have very light weed conditions, consider one of the progressive rake weed fins from True Ames (the Shallow Water Weed 39) or Tangent Dynamics Reaper Weed fin (from Sailworld) in the 32 or 35 cm sizes.
The progressive rake fins have a little less area and go upwind very well, but tend to collect a few weeds if the weeds are heavy.
The Lessacher Duo concept uses concave/convex surfaces on the same foil to cause all weeds that land symmetrically on the leading edge (LE) of the fin to "flap" in the concaves and they slide right off.
If you ever come down to Hatteras, look me up and you can try all 3 and see what works for you.
Hope this helps,