When you're not racing around the countryside for big$$ &/or world recognition, it gets to the point of asking how many angels can dance on the head of a pin.
For most if not all of us that aren't professional racers, the cheapest way to go faster is to get in better shape. I'm a long way from ditching my 25lb. steel bikes in an effort to shorten my commute times; my first priority would be to seek solutions to obstacles (e.g. weather, schedule) that keep me from commuting on a given day (hence getting more fit). I know this doesn't exactly addres the OP; but I really do question this weight weenie stuff for the vast majority of us, except as a status/bragging topic.