COP curves, or COP versus temperature diagrams, comes in many different flavors, evaluated by different methods. The three pumps used here have data taken in the same way, allowing performance and investment comparisons.
The data as given shows the heat pump COP at different temperatures. I have only received values for a number of those temperatures, although full diagramming should not be hard to come by. Anyway, to be able to use the data, I have elected to translate the discrete known values to interpolated COP curves for all temperatures in between. This is a process which introduces some accuracy errors, although in this case the deviations should be quite small, and not large enough to contribute with significant importance for the evaluation of results.
The diagram below shows the COP curves for three NIBE heat pumps (2020 series, 8 kW, 10 kW 14 kW, which have the same values as correcponding NIBE 2025 series heat pumps). The top curve shows a higher COP for all temperatures down to approximately 0 degrees Celcius. This means that for all days where it is warmer outside than 0, the heat pump with 8 KW is more efficient than the other heat pumps.
The two bigger heat pumps in turn are more efficent at temperatures below zero, although the difference in curves is higher above zero than below zero. This means that the temperature on your location decides which heat pump that on average will have the best COP curve, which corresponds to efficiency, and thus also best contribute to energy savings as a result of the investment. For calculations on energy savings based on selection of heat pumps, there is a form for doing your own energy saving calculations, based on heat pumps, COP, and current house needs and location.