What do you mean by "enough"?
Gear choice depends on engine load and road grade. And whether you're driving for fuel economy or not.
For fuel economy, I will occasionally "cruise" in 5th gear at 45 km/h, provided I'm on a level road or descending grade, and assuming I don't need power for acceleration (in which case I will downshift).
I often shift from 3rd to 5th after getting up to speed.
If you are talking about a flat, straight section of road, I may be in 4th gear at 40 km/h for better fuel economy. As I approach 60 km/h, I may slip into 5th gear for the same reason.
I find it easy to tell when my Mirage engine is happy & when it is not!
If it helps, I had a dodge aries(automatic) that did 80kph in first gear one time. It was also the last time that car went that fast cause it quickly became a 3 cylinder.