Not enough. I live just south of Washington DC and my last two homes have had heat pumps. They are/were relatively new, my current home's oldest unit is 5 years old. I'd have to double check, but they are of average, if not slightly above average efficiency. They suck at keeping my home affordably heated, not to mention comfortably heated. During the three coldest months, overnight temps are consistently in the mid to low 30s. We have times where we are in the mid to low 20s or below. Day time highs might be around 45. The colder it is, the longer they run and the less comfortable the house is.
Our electric bill was really high before I got the woodstove going - we moved into current house this past January.
I don't doubt you can get units more efficient than what I have, but that's going to be at significantly higher cost than 5k installed and I'm confident that they won't be great as a source of primary heat.
From
https://www.weather-atlas.com/en/maine-usa-climate:
"November to February, during the winter, is generally the worst time to visit Maine.
The night temperatures often drop to 0°F (-17.8°C) and sometimes even below, while the day temperatures are around the freezing 32°F (0°C) during the peak of the cold season. Maine winters are cold even during the day as the sun disappears for long hours, sometimes even for days."
And from (broken link removed):
"Still,
heat pumps are simply not ideal for climates like ours."