You have 2 carbon layers with area close to pi × 0.076^2=0.0181m^2, or 2× 240x 0.0181=8.7g weight of the carbon. Going to 90gsm will cut this value to 3.3g, or 5.4g lighter blade.
IMO, 90gsm is very thin carbon layer do give you additional speed. Ask @SDC, he uses a lot of types of composite...