NZ house builds on average are some what lower in efficiency that say Europe. Basically money is spent on size and not always on quality. A mindset change is required.
So your your ten hours running is this based upon, cycling over 24hours or thermal loading on set periods.
If the second when would you choose to run it.
If we presume again that the heating circuit and house insulation are the same for ground or air source.
Ground source is great in the right application, but in some cases it is not the cheapest method of heating a house in the long term. But this statement has to backed up or evaluated. Hence we need a starting point.
If SCT was the same for both sources, then it comes down to the SST.