Let me establish an argument here to keep things lively -
It takes no more power to take off down wind than it does to hover in still air. That means that the rules of thumb presented above (good ones, I think) are for you to use if you don't know what the capability of your aircraft is, and you have to judge by what you are seeing right now on a windy day.
The power rise due to downwind takeoff is never more than the power increase experienced between a windy day and a still air day.
The transition needed for the private pilot to move to the next stage is to begin to understand the performance of the machine against the charts, so the power needed on a given day is known before the liftoff to a hover. Then the downwind takeoff is a choice, not a chance.
