some comments:
1) Dave's idea of perfect symmetry is like a mantra to him, and of absolutely no validity from any standpint but his own. No physically symmetrical system has any degree of symmetry from the standpoint of forces and moments produced, due to all the other aspects that influence the aerodynamics.
2) He is all wet with his calculations about different rotor diameters and the ensuing loss of "symmetry" since the X2 has two identical rotor diameters, and blade sets. The illusion that ppruners have spun into a physical fact is just that, an illusion. The rotors are indexed so that they do not cross at the cardinal 90 degree points, so you see them as if they were different diameters. A gold star to IFMU for explaining this to Dave!
3) There is little similarity between the ABC/X2 and any other coax or syncropter, because the ABC type rotors are extremely stiff, with hinge offsets above 15%. This allows near stall maneuvering, a fact that is lost to those "expert" web sites that compare the X2 to a typical Kamov design.
4) The KA-50 has a hinge offset of 7.5% on the lower rotor and 2.5% on the upper, making the flapping motions quite large, and forcing the rotors to be very widely separated, with a great deal of drag (about 15% more than necessary). This low offset also makes the flapping near stall much greater, so that there can be little maneuvering at high speed, and therefore no high speed. In fact at least one and probably two KA-50's were lost to self-midair.