The Virgin Atlantic Global Flyer had the fastest average speed of 342.21 mph.
The all-composite Global Flyer was designed and built by Scaled Composites under the direction of Burt Rutan to meet the minimal demands of fuel for circumnavigation. It contains 13 tanks that hold 11,034 L (2,915 gallons) of fuel. Eighty three percent of the maximum weight is fuel. This enabled Steve Fossett to become the first person to fly solo and nonstop around the world.
Links go the the National Air and Space Museum Website: