for losing weight, i'd ditch:
the fork to get an "xc" fork ~.5-1.3lb off
the wheelset ~1.5-2.5lbs off (for nondisc)
the chainrings or possibly even the crankset/bb ~.5lb off
the disc brakes ~1lb off (including the rotors, if switching to v's)
the handlebar/stem combo ~.3lb off
tires too, although i'm not sure about what your current tires weigh, light tires are ~4-600grams IMO.