^Yeah, but you’re describing an academic issue re: “systems at equilibrium” that (IMO) really doesn’t exist in the real world.
Think: my experience is that it takes about 5 miles of driving to get the coolant to temp (with my new car, you can get “real-time” coolant readouts). Motor oil is NOT thermostatically regulated, and (from what I’ve read) takes longer to get to temp, and may NEVER get to temp in sufficiently cold air! (So, let’s be safe any say “10 miles.”)
Differential and MT are wholly unregulated, and I’d expect them to rise merely to a temperature N degrees warmer than ambient, where an equilibrium is established: within reason, they’ll vary directly with outside temperature. (AT generates enough heat to warm itself over time.)
So…you have a car that takes from 5 miles, to infinite miles, to fully warm! For a given application (such as “grocery getter”), the “warmed to equilibrium” answer is moot, as it never completely happens.
And there’s a few others: the denser air means you have a more powerful engine…which means more pumping losses behind a cracked throttle. Poor atomization is an issue (more so for carb than EFI, but still relevant).
But mostly, winter mileage is lousy because of the transient “warm-up” inefficiencies. A pre-warmed car that is never shut off should be a lot closer to summertime performance.
Re: “area rule,” supposedly the styling cues for the Corvette Stingray were cribbed from the area-ruled fuselages of fighter jets of the day…much like tail fins were cribbed. Area rule only matters if you have wings around the “waist,” and then only as you approach the speed of sound: any faster (or slower) and it actually hurts aerodynamics slightly.
So, in the end, just fashion…but really awesome looking!