The above table is intended to be used flexibly according to conditions and goals. Contrariwise, strong and especially well trained cyclists might be able go faster. Moreover, there is a lot to see on the parkway, versus just racing by it all. The attractions of arm-chair planning should not obfuscate the central issue that, before setting out on a trip, one needs to get into good enough physical condition to meet daily goals. I intend to do so by making several preparatory bike rides of at least equal intensity to the average anticipated daily parkway ride.
Health is a reasonable concern.
Jerry Bledsoe in Blue Horizons p.15 pointed out a Mt. Mitchell heart-attack death. Then make plans accordingly. Planning predominantly depends on wisdom, assessing conditions, and adjusting goals as needed. The first , this page. It combines the above table with other Parkway options and information .