As I understand it, the only way to address Boxster torsional flex is with a cage. Strut braces support areas of the car that are already quite stiff so don't add much. I still find the Boxster to be pretty stiff and precise compared to most cars. The only time flex becomes a real problem is when using very stiff springs so the torsional body flex becomes the new effective spring rate. The Cay is definitely stiffer and more precise though.
So many other areas of the car to derive performance before body flex becomes the low hanging fruit...
