The spax have a wide range of adjustment (24 point) from fairly soft to blody hard. Abviously they won't stop the back from sinking with loads of weight on the back axle. Its a case of stricking a balance when loaded and empty. I think I can probaly slove the coil over problem by getting some of the std spax modded to coilover.

I'll see how badly it handles. I was keen on the cheapness of adding springs as the car is rarely driven unloaded.