That is remarkable !
I drive at about the same rate of speed on highways,
and my percentage is about the same - maybe 70% hwy/30% city.
I'm doing good to get 50 mpg overall in a bone stock 89 4dr Jetta 1.6 NA. My best was 52.1 with 90% hwy/10% city - before i moved.
Giles definitely put you right into the magic zone.
I visited his shop about a month ago.
Very nice place and top-notch equipment.
Really good people.