If I'm hearing it correctly, I think too stiff of a ride is also bad on the frame. Struts are made to absorb shock energy otherwise absorbed by your body.

I think finding a good combination of spring and strut rate is important if you want to consider maximum stiffness

I say seek you efforts in the direction such as Progress or Teins coilovers as they manufacture racing products for street use. They are stiff as fu#k on a supra that a friend of mine own (Teins).

Hope this is somewhat insightful.

-K-