My Dh and I are doing the Chuckanut Century also! The South Route looks to be a reverse variation of the Skagit County Classic ride--at least the metric century route, which I've done--and then another loop and an out and back which I'm not familiar with. You can play it by ear and see how you feel after the big loop and see if you want to ad on more. The north route appears to be much flatter, but we know from experience to expect ferocious headwinds. We're going to do the north route, metric century on our tandem. If you see a big blue tandem with a fat lady on the back, that'll be me!