Check the manufacturers websites. The Europeans are ahead of the game. They have been making medium to big bore dual sports for years. See KTM, Husqvarna, Husaberg, Aprilia, BMW, CCM, Gas Gas. Some of the bikes from Japan are already set up for dual-sport also. See Honda, Kawasaki, Suzuki and Yamaha. Some of these Japanese bikes may require minimal add ons to be fully street legal, based on your state DOT requirements and most of the Jap bikes are only 5 speed transmission types. You say,"a 250cc is just a bit small for toting a load of gear". Let me remind you a "Dual-sport is designed to ride on the street and on the dirt. It is not classified an "Adventure Bike". Most real dual-sport riders carry what they need in a back pack or a tank bag or tail bag. You say," 650cc is just a bit clumsy in the single-track. I think that is only relative to a riders ability and the degree of difficulty of the single track or it's condition. The Dakar bike are in a different universe compared to a dual-sport. They are "Full blown RACE BIKES" and don't believe any different. Also believe the riders who compete in the Darkar type races are World class riders.