You might want to check out a ride called RATPOD. Ride Around The Pioneers in One Day. It's in Dillon MT in June. A benefit for kids with cancer. Something like 157 miles and 7500 feet. Really beautiful route. Lower numbers of riders. They have a good website, and I know a guy who did it...said it was a great ride.

Edit: PS, you might want to check out the Shasta Super Century. Only 130 miles, but 16,000 feet of climbing for a challenge. I did the century this summer, and the riding is GORGEOUS.