Noticed that you are carrying the PSS9's now. There is a thread on the RX8club forum with regards to them, the actual spring rate seems to be a point of confusion, several people have received vastly different information on the spring rates from Bilstein people themselves. One with the rates that you have listed and one in a much lighter rate, closer to that of the PSS10's. Just thought I would mention it.
It appears that the part #'s on the PSS9 & PSS10 springs are the same.
Rear main: E4-FD1-Y805A00
Front main: E4-FD1-Y412A00
Front helper: E4-FD1-Y504A01
if that means anything.