From what you say (this post and your other post), it seems to me that they have an easy half standard, a hard half standard, a metric, and the full century.
I signed up for the century on the website. I figured since I know they have 2 different half-centuries to choose from and only one option on registration, that it would probably be fine to sign up for century and then decide which century to do on the day of the ride, metric or standard.
I'm liking your idea of weather analysis before deciding which ride to do. I was going to decide last Saturday based on a long training ride and how it went, but that got rained out. From looking at the routes, it looks like the metric and standard centuries are on the same route up to ~42 miles in, where you could theoretically change your mind I guess? Same with the 2 half-centuries, they're the same route for the first 25 miles before they both split off from the century routes and from each other.
Also, mapmyride and ridewithgps have very different elevations for these routes. It's disconcerting that one shows 3500 feet and the other shows 5400 feet of climbing for the same route.