I dunno! I only drive 70 mph a few times a year, when on long (multi-day) trips.
The rest of the year, I toodle along the scenic side roads at ~50 mph / 80 km/h.
But theoretically, an unmodified
5-speed Mirage is good for ~42 MPG US @ 70 mph on level ground in warm weather.
The Metro/Firefly (unmodified) is about the same.