I've been using two heat pumps near Austin, Texas since 2011, rated at a total of 84,000 BTU/hr (4 ton + 3 ton capacity) (25KW of heat) on a total of 5KW electrical input (COP ~= 5.0).

They are standard outdoor air heat exchangers so below about 35F efficiency drops significantly. That's pretty rare around here so it is almost always enough - we can still gain about 45F vs the outdoor temperature even below 20F.

We don't have natural gas available where I live, only propane. When I purchased the heat pumps, propane was $5/gallon for 91,500 BTU. That translates to about $4.60/hr to run 84,000 BTU/hr of furnace. With electric energy (cheap in Texas!) at about $0.11/KWh, the equivalent costs of my heat pumps was and remains close to about $0.55/hr to run.

In the summer, they cool with equal capacity and similar power consumption for a 15 SEER rating (waste heat from the system components works against cooling in the summer!)

Factor in your acquisition costs (mine, just after the housing bust and with a little legwork, were about 20% of retail at the time, so a no-brainer) and you can get a lot more objective idea what you're really accomplishing.