can see them installed for 70 to 80 percent in some extreme climates. Could work out to 90 to 95% of the heat you need each heating season comes from the ground 5 to 10% the auxiliary heat working on top of the geo unit
where i used to live you could size them to meet the entire heating load but it was like diminishing returns. Those sized for the full load were way oversized for cooling.
Where I used to live was not very humid in the summer so never had a high humidity problem from the over siizing. May be different in your neck of the woods
You need to talk to someone who knows the 'bin weather data' for your area