Toyota Yaris Optimal RPM for Highways

[Anquietas]

Hello,

I have a question regarding the basic operation of a Toyota Yaris when cruising on a highway.

I own a Toyota Yaris 2010 model, living in Europe/Romania, with the following specs:

VIN: VNKKH98370A089720
Engine: Dual VVT-i 1.33 L
Capacity: 1329 cm3 (74 kWh)
Fuel: Gasoline
Redline: 6200 RPM
Max: 7500 RPM
Max Torque: @ 4000 RPM according to the datasheet
Transmission: Manual, 6+1 gear

My question is:
I need to travel on highways in the near future.
What is the OPTIMAL RPM for Cruising on Highways ?
(I do not want to cruise as a snail, but also, I don't want to race like an F1 car either).

I am talking about cruising safely on the highway, with no thoughts of engine wearing or damaging components and optimal fuel consumption, if possible. If not, let's say fuel is not so important. I am more concerned about cruising at safe RPMs while also reaching my target in a reasonable time.

As I understand, if cruising with more than 4000 RPM (after the Max Torque threshold) the car begins to loose power and efficiency, and after 6200 we meet the redline.

In the 6-th gear @ 3000 RPM it cruises @ 120 Km/h (tested by me)

So, what is the optimal RPM for normal cruising without having to worry about engine damage ? 3000, 3200, 3500 or even the max torque ?

Thank you !