Nemesis Champion Racer
Three major reasons:

1) Advanced aerodynamics using CFD analysis and wind tunnel testing as well as construction with lightweight and largely seamless composite materials provide a very 'slippery' airframe that doesn't create a whole lot of induced or parasite drag for a given speed.  Very thin, high aspect ratio wings are used.  Access panels are kept to a minimum.  All joints are smoothly blended together.  Landing gear is retractable and fully enclosed.  Fasteners are flush and heads taped over.   Gaps and edges are puttied or taped sealed prior to flight.  The airframe exterior has been waxed and highly polished for as smooth of skin as possible.  The entire aerodynamic envelope has been very carefully studied and optimized to minimize areas producing turbulence and as a consequence parasite drag.

2) Minimized flat plate area.  The cross section of the aircraft has been kept to the bare minimum needed for structures and systems and virtually nothing for crew comfort.  The cockpit is really tight and built around the shape of the pilot's body - even to the point of requiring the pilot wear an oxygen mask connected to a fresh air vent to facilitate breathing.

3) Sacrificing docile handling characteristics.  The wings and flight controls are maximized for high speed flight as opposed to easy and forgiving flight characteristics.  If you look at a Beech Bonanza or a Piper Archer, you'll note that they have very thick wings which handle well at low speeds and give an inexperienced pilot a lot of forgiveness in sloppy handling before departing from controlled flight at the expense of producing a lot more induced drag.  This isn't the case of the Nemesis and it demands a very good pilot at the controls to fly it at the correct speeds and numbers with little margin of error.