[dcb]

Like it or not, most people are basically on a set route during commuting, and don't do a whole lot of research about which route uses the least gas (or which route enables the most gas saving technique even). Similarly, you do not see a lot of people seeking out the most efficient route to the store and back, or to piano lessons or whatever. So MPG is simply a measure of efficiency of the driver/vehicle overall, not a measure on how good a route planner they are.

You absolutely can use raw fuel consumed to locate the best route between two points with some trial and error. Keep in mind that the best route may change as your hypermiling skills change and equipment gets modded, but yes the bottom line is how much fuel did you use to get from point a to point b.

If any driving is jeopardizing your mental health, then you should chill. Don't be in such a rush that you go wacko over the slightest obstacle. Most times folks have to slam on the brakes is due to bad planning (and braking is not efficient). And as you learn what hypermiling actually is, don't be surprised if you find yourself saying the exact opposite of this "I know that MPG will probably be better on the highway". My cars have not been aeromodded enough where I do better on the hiway than in the city.