?
Nick sez;
TR's "lose" about 3% of the power that the helo has.
CRAN sezed;
Representatives of the Kamov company have been present at the last two big UK Helicopter technical get-togethers and on both occassions have claimed that the co-axial rotor configuration, when properly designed is in fact more efficient than a single main rotor and tail rotor configuration. To the tune of about 15%!
Western spin versus Eastern spin?
More spin. 
Dave