I have the Ford lower brace but haven't upgraded to BMR or Steeda bracing. So far, the car handles extremely flat >1G. Though my suspension likely has a lot to do with that as well.
Does the S550 convertible have a factory K-brace and other unibody bracing not found on the S550 coupes? If the verts do have other bracing, can it be used on the coupes?
Back in the 80’s-90’s, we used to take the convertible K-bracing and the rocker reinforcements off the Fox verts and install it onto the equivalent notchback and hatchbacks - factory parts that worked to stiffen up the unibody, as well as using the aftermarket frame rails and strut tower braces.