I'm sure gear selection had something to do with what's available.
But if you look at a dyno curve...

You see that the torque curve is quite broad, top 10% goes from 2500 to 5500.
Whereas the top 10% of hp only goes from 4500 to maybe 6200.
We can see from the speed chart peak torque occurs from 60 to 70 mph in 5th.
I hear that's optimum for mpg.