There’s an annual ride called the Cheaha Challenge - 100 miles with almost 10,000 feet of elevation. I’m not sure I’m ready for that. The North Jefferson Century with 5,000 feet of climbing nearly killed me in August.
I've done Cheaha 2 4/5 times -- the first time I did 84 miles, to the top of Cheaha and back again (normally you go over Cheaha, down the other side, then back up over Cheaha.). It wasn't as bad as they make it sound. Much of the climbing is up and over Cheaha Mountain twice. I'd recommend trying the 84 mile option if you're unsure, but really the extra miles don't add too much pain. If you're already breaking the 6 hour mark, then you're ready.