Forgive me, but why it is valued so much to be THAT far underweight. All I can think if is that you've made a design error. Because those 5 kg of lead you'll have to hang of the platform will do a whole lot less for performance and feel of the boat then including those kg's in extra platform stiffness, stiffer beams, impact resistance, stiffer daggerboards, stiffer rudder setup, reinforced keel line or even heavier and cheaper components in the way of blocks and lines.

I never understood why some sailor pay top dollar to get special lightweight lines and blocks only to add a few kg of lead before racing.

Wouter