Any published powerbands will be for full throttle. But generally you don't drive around all the time at full throttle. A lightly throttled (loaded) engine runs more efficently at lower engine speeds. Heavily throttled (loaded) engine runs better at higher RPMs. A lightly loaded engine turning high rpms is wasting a lot of fuel just to spin the engine. A heavily loaded engine at low speeds (lugging the engine) creates high cylinder pressures and requires a rich air/fule mixture to keep the engine alive.
So you have this double edged sword. by running without an overdrive you turn too many RPMs and are wasting fuel just by spinning the engine. Go to overdrive and lug the engine. The balance between the 2 points is what gets tricky.
As for the powerband I spoke of earlier, you just need to drive the vehicle and feel the engine. How well does it run at low speeds with some load on it? Too much load at too low of a speed and it isn't happy. Then you need to guess how much load you have at cruising speed and figure if the engine will be happy pulling that amount of load at the RPM you want it to run at.
I am sure there is a science to it, but it really comes down to how it feels to us.
My torque built 351 is happy running 1000 RPM under light load and at 2000 RPM is completely happy pushing my brick down the highway.
Another project with a stroked 302 hates any load under 1500 RPM but is ina a body that goes down the highway much better. It still cruises nices at 2000 RPM. But that cammed and stroked 302 would not be happy pushing the bronco down the highway even though it is the same RPM. That is because the load is higher in the Bronco. Again, a balance...
Throw in a bunch of variables, how flat are your roads? how fast do you want to drive? engine size, cam, etc...
This will be debated for a long time. Why? There is no clear answer. If there was then this wouldn't go on forever. The answer would be given and the thread would end. But no, the debate about gearing will go on forever. Often with what some people think is "perfect" while others with the same gearing hate it, often for completely different reasons.