In the UK on carpet the grip often comes up enough to use Greys in Mod, the Parma greys actually feel softer than the pinks.... I was goign to test them back to back last night but smashed cars up instead.
Apparently Trinity do a spacer for the rear axle but it is no different to running a pile of shims.
For a fanatastic L4 guide read Mike Lufaso's site, link in post a few above. The shock pre load is used to get the ride height correct, or really I guess to get the chassis level once you have set the ride height at each end with shims at the front and the inserts at the rear.
-Scott