I followed the Cape Dory 28 news for several years when I had a CD28 gasser. I never heard of a CD, whether gasser, Westerbeke 100 or Volvo 200 that was propped significantly wrong. No under propping was reported (wot rpms higher than rated max) and a few with slight over propping (rpms less than rated). The latter will give you a false sense of better speed but at greater engine harm.
David