Disclaimer: John's in a crabby mood the last couple days.
My opinion is that Old Macdonald is a little tougher walk than Pacific Dunes, because you climb up and down two significant dune ridges on holes 3, 7, 14 and 15. The green to tee walks are very short, though, maybe only 50-70 yards away on average.
Pacific Dunes has a couple of longer walks: 3 to 4, 17 to 18, and especially 11 to 12. 13 to 14 is a short, steep climb.
Chambers Bay's routing is much more sensible when playing a normal yardage (6500 or so yards). At that distance the only long walks are 3 to 4, 9 to 10, and 14 to 15. But it's hilly, and a harder walk than Pacific Dunes. C'mon man!