There are two types of rear spring for the estate depending on the type of shock absorber. The Nivomat self levelling shocks have an integral spring so the main suspension springs are softer. If you fit standard shocks (as I have) the back end will sag, particularly when loaded. Heavy duty springs (from GSF for example) will sort this out but I do find that the rear is now slightly stiff and bouncy when not carrying a load, but it sounds as if this is what you are after. HTH