The century is a difficult route given its length and total climbing but, the grades are very manageable. Unfortunately, the metric route omits the premier parts of the century route - much of which is on the Parkway, and probably the most scenic section of Parkway in all its length. I would recommend the century, and starting an hour earlier or resigning yourself to going slower and taking more breaks if necessary. Take it easy and enjoy it, and stop for pictures because the vistas are gorgeous.

If you are training for a century on Labor Day, then you should be riding centuries now.