One thing that should be pointed out here is that R22 and R410A do not have "efficiencies". They have different thermodynamic properties that require different operating conditions (temperatures, pressures, etc). There are slight differences in heat capacities, but a well designed system for each should minimize these differences in operation.
Bottom line is that the greater efficiencies today are mostly a result of increased mechanical efficiency in the compressors, larger area condensers and evaporators, use of TXV expansion valves, etc. The highest efficiency units rely on dual or 2 stage compressors and multispeed fans in the indoor and outdoor units, to better match the workload required to the input power. A compressor or fan is normally sized to operate at maximum efficiency at full load, and reduced loading lowers efficiency as fixed losses become a greater percentage of the power being used. The refrigerant is a very small factor in the overall equation.