The ride height needs to be known before you order the shock to a degree as they come in different lengths and there is only a few inches of adjustment on them.
I don't know if ti is a problem with the red9 units, but remember if you go stiffer, the spring diameter will increase so you may get clearance problems...
red 9 have a small section on
www.volkszone.co.uk a search will bring it up...
Rich