This really seems like a nice application for the Qranium when it comes out. It could tell you your target based on where you are on the course. The research behind that target is in its infancy, but this would be a good tool to start figuring that out.
Actually, the ibike might be an even better head unit with an ANT+ Sport PM because it will actually measure grade, and will have some idea of the relative wind speed. Analysis would have to be done at home, but it could be a good research tool too.