What if you were driving into a headwind? Theoretically couldn't you add more power then it cost from weight and drag?
Then of course you would need a big spinnaker for the other direction. We need wider roads so we can tack as well.
Actually I just watched a different blackbird video that shows the physics. I may need to eat my sarcasm
http://www.wired.com/2011/02/ff_fasterthanwind/