[muzzza]

TL There are a swag of reasons why you should never have the same spring rates front and rear. Spring length does not change ride height. If you wish to raise the car, you can use stiffer springs, longer shocks, or lower your upper spring mounts. Crazy amounts of spring pre-load is not an option. QA1 make 1" and 2" shock extensions as an alternative to purchasing longer shocks.
I am using 17" QA1 DD shocks and 10" springs on the rear of my car and 15" QA1 DD shocks and 10" springs at the front. I have also dropped front upper spring mounts about 10mm giving about 15mm extra height at wheel ( 18" rim )