Intersting read around shocks and springs, always thought Koni is a lot more expensive then Bilstein, but the price is the same, actually R150 cheaper then Bilstein.
I put bilsteins on my 840 only because I could not get original shocks anywhere so went with the bilsteins and I'm seriously impressed, works extremely well with the heavy girl.
Ok, M5 Sachs and Boge shocks were never released by BMW for aftermarket production......dealer only!
The plot deepens.......there is a Sachs shock that fits, awaiting price!