Dave,
Early helicopters all had low disc loading and probably autorotated well.
In my mind, two rotors are less efficient than one. Just like two wings are certainly (biplane) less efficient on an airplane.
If I could, I would go with one blade. The working part of the blade is near the tip. The inner part is mostly just there to support the outer part. A twin rotor configuration has a higher percentage of useless inner rotor.
In other words, one large rotor will lift more pounds per horsepower than two smaller ones.
Headsethair,
That Bladerunner sure is stable in a hover! The blades have too much pitch to auto unless you get the rotor to reverse rotation. Take the rotor off and drop it from the ceiling and it will spin in reverse.