I found some charts from research on Sheldon Brown's site about rider speed vs. wind from different directions, and it backs up that you can not use a tail-wind to make up all of the losses incurred fighting a head-wind. Looked pretty legit. Info on whether going down a hill can make up all the loss from going up it seems harder to find.
One thing the Sheldon Brown site says is that a headwind from the front 200 degrees slows a rider down, while a tailwind has to come from only 160 degrees to be helpful, so not being a 180/180 split right off the bat puts the rider at a disadvantage.