Let's really revisit a topic from the past. About 3 years ago I did this rough calculation that BMW could save about 300 lb in the F8X M3 by going to an all CF chassis (read whole thread). Seems like that calculation was very reasonable in comparison to the 286 lb saved in the new CF 7 series chassis. Although this weight difference is not only due to the chassis alone but it is the largest component of the savings. My rough calculation also assumed a nearly complete CF chassis, which clearly is not the case here with the 7 series either. These errors/approximations are both consistent with the <300 lb actual achievement.
7 series info
here on CF chassis.