Between expensive tickets, horrible lane discipline, and so many trucks on the 401, it rarely makes any sense to do more than 120 kph, At least in my area (Windsor - Kingston). Pass and wait, repeat.
With my 2022 Corolla, the sweet spot is 120 kph for speed and efficiency.
My Mazda 6 Wagon was an amazing highway cruiser. If I remember correctly, it was turning over at 3K going 140 kph, it ate up the miles.
Wind is a huge factor for f/e. You can lose 10% for every 15 kph of headwind. Then add in resistance the faster you go, which is exponential (or was it cubed?).