Mark H. has given you a good suggestion.
I use the Lessacher Duo Formula weed on all boards wider than 86 cm and they really handle big sails
=> 9.0 at only 40 cm depth.
Others you may want to look at are the True Ames Santa Barbara weed or Shallow water weed in > 50 cm.
Also the Tangent Dynamics "Reaper" in 46 cm does a good job on a formula board (or any > 86 cm wide
board for that matter.
Hope this helps,