How low to go in the front

I have seen Dan’s formula for the amount of saddle-to-pad drop on a tri bike. Is there something similar for a road set up? Right now I am have a saddle hieght of 75cm and a drop of 9.5cm (saddle top to bar top).

BTW: Speaking of front end drop, The article on Andersson’s P3C with the proto aerobars seems to have vanished.