Re the Tango (composite) and RV (metal) an article in July Sport
Aviation (pg 54) addresses Drag Coefficient as a function of
construction process. The multiplier for the Drag Coefficient for
composite is 1.0-1.05 and for flush rivet metal is 1.10. Composite
can reduce drag then by 5 - 10% over a metal constructed aircraft.
Food for thought.