20 lbs, even at the end of a 6' CB....
...probably wouldn't make much difference on a boat with 2000 lbs water ballast, and if you put enough weight on to make a difference you wouldn't be able to raise the board. I know a guy who made a replacement centerboard for his H26 out of heavier material, and had to abandon it because the short travel length of the control line made it impossible to raise it. Rerouting the control line is not an option because you'd have to penetrate the ballast tank. IMO, the boat sails very well with the reefed main.