I'm basically in the same position living on the coast of North Carolina. One thing that I've noticed is that I tend to try to pedal harder into a head wind. I think I do this pretty much on a subconsious level. Regardleess, it tires me quicker. When I force myself to maintain a doable cadence and just accept what the wind will give, seems to keep me sane and not completely worn out.

I'll think about the wind and speed and aerodynamics and friction and Einstein the next time I'm drafting with ease behind a big group.

There is a force requirement to move mass AGAINST A RESISTANCE, such as air resistance, bearing resistance, or the rolling resistance of tires. Climbing can be seen as a form of resistance. In Newtonian physics no force is required to maintain speed of motion if no resistance is present. In relativistic physics this is not the case, but the additional forces would not reach a level that is significant until the speed becomes at least maybe 20% of the speed of light (depending on what you think "significant" means). At our piddly little on-planet speeds of travel, even fast cars don't go more than about 50 meters/second. The speed of light is 300 million meters per second. Special relativity has essentially nothing to do with us.

You have no idea how much that helps!

That explains everything. With anything but the very slightest downhill the energy assist from gravity far outweighs mechanical losses in our bikes. It's rider effort plus gravity against mechanical loss and the wind. If the hill is steep and long enough gravity alone will be enough for us to reach 30 MPH.

Riding into the wind on the flat our lower speed reduces mechanical losses but not by nearly enough to compensate from losing that wonderful force of gravity. It's just us against the wind unless someone will provide a draft.