Dave,
While thinking about your idea I came upon a variation on the same theme that you might like. Your initial idea comes from the basic fact that bigger rotors are better at a hover and smaller are better in foward flight (turned to act like a prop). Folowing those same lines what about using an intermeshing design? If you take a intermeshing rotor system with the rotors set at an angle to each other and then rotate them both forward for fast flight then each rotor would only "see" a portion of the oncoming airstream (think Kmax with short stiff rotors flying nose straight down). I guess it is a bit like a full size rotor flying edgewise through the air like a traditional helicopter just without the disymetry of lift or a need for a pusher prop. You would have a disymetry of thrust as the advancing blades would be either on the top or the bottom of the discs now but that may be useful depending on the design. I don't know how much of an angle to each other the rotor would have to be in order to get any bennefit in forward flight (or if the theory would work at all for that matter). Getting the whole ball of wax to rotate around a set of wings would be a bit of a trick as well but I originally thought of this as a tail sitter arrangement but I'm sure it could be made to fit another set up.
Yeah yeah I know...I should quit thinking and drink more right!
Max