I have the CSS discs and TTRS 4 pot calipers. The calipers weigh in at 3.4kg without the pads in and are a big improvement over the R brakes, which are single pot, made of cast iron and weigh 9.3kg without pads.
Almost 7kg saving per side.
Wheel weight doesn’t do much for economy, but for acceleration and deceleration the effect of saving 1 kg per corner is the same as taking 20kg out of the body of the car. Lighter wheels also give a better feel in my opinion to the steering. Currently I have 5 sets of wheels...yes I have an alloy wheel fetish. LOL.