Wheel and bumper weight differences

How many lbs weight savings going from a set of Rallyes w/centers and caps to a set of alloys? I know this could be subjective, so I'm just wondering in general. I also have read about unsprung weight- so I'm guessing wheels would be in that category. Wonder what if any difference any weight savings here would reveal?

How many lbs could one expect to save using plastic bumpers and alum mounts?