i will check Amazon for books.

Therefore both torque and RPM should fall off with increasing RPMs.

Why is a flat torque curve important?
With most HP curves seem to have a upward slope while the torque "curve" is usually flat.

Not to be disrespectful (this being a website for us mercedes benz fan) but I too think the subaru flat 4 is a remarkable engine and so is their AWD system.
But then again they have had many years to finetune that engine and system.
In the same way that Porsche has had with their flat 6-essential unchanged in 30plus years.