As soon as Bilstein has something ready for the S550, we will be testing it.
Right now the cost to custom build a complete S550 strut using generic Bilstein Motorsports components approaches or surpasses the cost of a MCS (Motion Control Suspension) kit. The MCS setup would be a better kit with more features for about the same cost.
To keep the prices reasonable, we have to start with an OEM fitment Bilstein strut and then test it's limits for something like the StreetPro kit, or modify it for something like the TrackPro kit. If the MCS kit was not available, we would go ahead with the Bilstein Motorsports kits, but I'm not sure there are many people who need a set of $10k double adjustable inverted Bilsteins, or even a set of $5k non adjustable inverted big-piston struts. If that's you, or you plan on doing gravel rally events, then give me a call because I'll build them. But for most of our customers the MCS is a better price-to-feature balance.