I tried the double, I failed. I am a big guy and the hills in the first hundred did me in, I live in a flat area so I was unprepared in addition to having to lug my beer gut up hill. Next year I will be back, lighter and better prepared because failing at that ride still bothers me to this day, but I digress. My friend however completed the ride, 16 something pace, in preparing for it he just rode alot, on a fixed gear. Did the ride on a geared bike though. The longest training session we did was 123 miles a few weeks before and then 95 the next day, that was tough. We also did a couple centuries in the weeks before in addition to other long training rides. The ride was in June I guess we really started preparing in late February. Check out the Book of Long Distance Cycling, I think that is what it called. It seriously is much tougher than a century is certain aspects and in other aspects you just do what you do for a hundred miles twice, like food and stuff. Just ride alot, and good luck.