Kalen:
To be honest, I've never measured the total walking distance of our courses that accurately ... I only pay attention to the individual green-to-tee walks, and whether there are more than a couple of longer ones.
And, obviously, whether you are going up and down hills makes a big difference, too.
But, I suspect you are right that once you get near 5 miles on the straight and narrow, the course would be perceived as tiring to walk unless it was very flat.
Which tees were you using to measure the walk? On some courses, back tees require extra hiking back, but the middle tees are an easy walk ... on newer courses, the back tee is the closest to the last green, but everybody has to walk the entire 7500+ yards.