I definitely agree with everyone else. It is sooooo much easier to do 100 miles on a well supported organized ride then even 60-70 on your own. Part of the reason I sign up for so many rides is I know that I'll do so much better because of the well timed stops with plenty of food and drink that I would never do on my own.

When I did my first Century of the year in June, I hadn't ridden more than 65-70 at a crack, and I had no problems with the 100.

At this time on the year in the Midwest, you'd better take a nice weather opportunity when you can get it. It doesn't mean that you can't still do the other Century.