[M_a_t_t]

Are you reinforcing a metal (steel?) skeleton for the reduced weight or just resin and carbon fibre?

I don't know the characteristics of carbon fibre, but I would atleast compare the compression and tensile strengths of the materials.

Theoretically you could reverse engineer the control arm to get the total resistance to deflect/bend in up/down and forward/back. The design of the control arm will reflect the characteristics of the material.

Then you could use the numbers for carbon fibre (and reduction % if you think safe to do so) to design the replacement.

The weight will depend on where the resin/fibre is. I don't think that a weight number is enough information to give any kind of reasonable answer. E.g. if you made a flat plate that weighed 50% the control arm it would probably snap. I doubt that a 1/4" carbon fibre plate will support the car. So redistributing the weight so that more of it is vertical will increase strength in the up/down direction