I have also received the same information as Roberto quoted, direct from king springs. (They were quite forthcoming with info)
I decided to go with the 160lb (f&r) Lovells springs as I wanted linear rates f&r. They are also supposed to drop the car by around 30mm but I believe they have actually lifted slightly. (I didn't measure sorry)
It would be relevant to note that I combined the springs with the "factory replacement" kyb gr2 struts, which wouldn't help trying to drop the car.
EDIT: To clarify, my car is a 240z