"For reasonable fast forward flight, my money is on the ABC-rotors over the tilt-rotors."
Agreed, but there are many dynamic and mechanical problems to overcome first.
"For very fast forward flight, my money is on Reverse-velocity-rotors over the tilt-rotors."
Agreed that seperating thrust and lift function allows the optimum design and diameter (as you pointed out) of each system.
"The next question then becomes Coaxial, Interleaving, Intermeshing or Side-by-side?"
Well, pure interleaving is still on shakey ground, for same reasons as V-22. I would wait to see how Sikorsky get on, regarding rotorwash dynamics, and keep Stepniewski intermesher in mind.
Mart