Yes, a discussion on the effect of a headwind is there, but I'm afraid the answer isn't.  So I put together a calculation that figured it out for airspeeds typical of my ES.  It turns out that with zero wind it is always more efficient to slow down, at least compared to any "normal" cruise speed.  But to be more realistic of what most of us might consider important, I typically us a number I call "effectiveness", and that is the MPG times the speed squared.  After all, most of us value speed quite a bit.  For effectiveness, you generally want to go fast.  For best MPG you usually want to add around 1/3 the headwind component to your speed.  For me, that means that while best MPG might be at 120 TAS with no wind, I would want to add 20 (maybe even 30) knots if I have a 60-knot headwind.  But above 140 to 150 TAS, the MPG is always going down with increased speed, regardless of any reasonable headwind.  I never fly as slow as 120, so it means that going faster always reduces fuel economy, headwind or not.  As far as "effectiveness", going faster gets to be a LOT better with a headwind.  Yes, go faster into a headwind, but I don't think that means going from LOP to ROP - that doesn't get enough speed to pay for itself.  And with a tailwind, definitely slow down - but I have a mental problem doing that!

Gary Casey