Any distance is good and esp. if you have someone fun to ride with. Looking over this thread, I've ridden part of the Grand Tour Double with CbadRider (not her real name), most of the Central Double Century (Litchfield, IL) with Richard Cranium (not his real name), part of the Knoxville Double with Homeyba (not his real name) and several doubles with Dante (that is his real name!).
Honestly, it's Mr.Beanz I'm concerned about. For six years now he's been talking about riding a double, talking about the CA Triple Crown (at least 3 doubles in one calendar year), but not actually riding any. Not that he doesn't ride, he does, and he rides well (sometimes shooting video as he rides), but he really needs to just do this doubles thing!
Rick / OCRR