I was thinking (bear in mind it's 4:45 AM) that the 200 K this weekend would be a good training ride for the folks considering the Davis Double. I rode the 200K in 2006 and it's 131 miles, 4700 feet of climbing. Especially if you have never done more than a century, it's a good way to ease up to the longer mileage on a pretty well supported brevet.
It's an out and back route to the Grange Hall, so you do both sides of Cardiac, which isn't as bad as it sounds..
Davis does take day of sign ups. Start time is 7 AM. You have 13.5 hours to complete the ride. It took me 9:37 in 2006.