'Hour power' would be a slightly better indicator of power at LT than 20 min power, since the longer the effort the smaller the 'contamination' from anaerobic capacity. OTOH, people often do sustained 20 min efforts in training, but only the true masochists go all-out for an hour. <g> So, it's a trade-off. The one thing I would say is that there's probably not much to be gained by including both 20 min and 60 min data in the table...the purpose is to provide a measure of a rider's relative strengths and weaknesses, based on four durations principally reflecting *different* physiological characteristics. By comparison, the extent to which your power does or does not decline more or less than average as time is extended from 20 min to 60 min (or longer) is a more subtle issue, and one that I don't think is easily or appropriately addressed using a table such the one I put together.
As for the relative decline across time as a function of the rider's ability, in general you would expect that the best road cyclists would tend to show the least decline between 5 and 20 min (and beyond), since that is a function of their LT (really, their critical power), and LT is the most important physiological determinant of endurance exercise performance. OTOH, you would, on average, expect an *inverse* relationship between the two left-most columns (i.e., 5 s and 1 min) and the two right-most columns (i.e., 5 min and 20 min), since the physiological traits (e.g., fiber type) contributing to very high short-term power would tend to be opposite those contributing to very high sustained power. IOW, the table should not be read as indicating that all riders of a given performance level/category show exactly the same rate of decline as indicated by the averages.
BTW, the top of the 5 s chart is based on Sean Eadie's known performance, whereas Arnaud Tournant's data was the source of the top of the 1 min column.