How much does tire pressure really matter?

[OakLeaf]

Just saw this summary of an article from Bicycle Quarterly from a couple of years ago.

Unfortunately the test protocol isn't online (even for purchase). I'd like to know more about it before taking it as gospel (how many riders participated, how much did each weigh, geometry of each bike and how many different bikes in each class were tested) - but it's interesting anyway, and I'll experiment with lower pressures now that I'm getting back on the road bike once in a while.

Anyone have access to old issues? Be sure to read the comments, which include a lot of participation from BQ's editor, apparently the test author, as well as some strenuous discussion of a conflicting test. Most interesting to me is the author's belief that higher pressure FEELS faster, possibly because of the higher frequency vibration translated through the bars - but doesn't actually result in higher speed at the same wattage.