to wit: a high school golfer averaging 80 on a moderate course is pretty commonplace. my brother, a 9 handicapper, was 4th or 5th man on a mediocre high school team. he will be fortunate to make a mediocre Division 3 program.
this career progression seems to parallel with somewhere around an 18 minute high school 5k. therefore, i suggest that an average score of 80 is equivalent to around an 18 minute 5k.
on the mercier table, this equates to just under a 3 hr. marathon, though in my experience, an 18 minute 5k is closer to a 3:10-3:20 marathon.
note: breaking 80 ONCE has no equivalent in running, since it is far more unlikely that someone will have one extreme performance outlier and nothing else in the same ballpark.