Gary,
I am using 80mm with 2mm wall on the Blade prototype and the tortional measurements I have done compared to other boats indicate it is quite stiff.
I am not using high temper beams. I'll pick up some of the stiffer Aluminium beams from AHPC in a couple of weeks.
Given the stiffness I'm getting with the softer beams
you may not get the improvement you want by fitting carbon.
Also I understand they didn't really get the returns from carbon until they started gluing them in.
If you do decide to go carbon please measure the tortional stiffness of your platform before and after.
It would be interesting to quantify the outcome on your platform.

I know that the voices in my head aint real,
but they have some pretty good ideas.
There is no such thing as a quick fix and I've never had free lunch!