GP meant that you are paying $5.80 for a therm's worth of electricity, so therefore electric and gas are the same cost at a COP of $5.80/$1.60 = 3.65. At a higher COP electric is cheaper; at a lower COP, gas is cheaper.
You can use that number when looking at a heat pump's datasheet to see which temperatures the heat pump would be cost effective for you.
No I'm not; I'm literally looking at my last gas bill right now. I'm paying $0.8309/therm for gas and $0.8945 for delivery services. That's $1.7254/therm, not $5.80/therm. (At $5.80/therm, I’d have upgraded a decade ago [or switched the house back to #2 fuel oil]!)
At 85% efficiency, that's $20.30 per million BTU for gas. *
Looking at the only maker of split-system air-to-water heat pumps in the North American market, their spec sheet COP** at 120ºF leaving water temperature is 3.33 at 45º outside air, 2.86 at 35ºF, 2.42 at 25ºF, and 1.99 at 15ºF. For February, that looks like I'd expect a BTU-weighted COP of around 2.5-2.6.
All from a system that would cost me around $15K additional out-of-pocket (after incentives) and would save a few hundred bucks in the shoulder season and cost me a couple hundred extra across Jan and Feb. $15K and less comfort on the coldest days to save $100 per year is a pretty negative RoI. $15K invested in Treasuries has a higher (and more certain) return and is liquid at the end, not thrown away.
* https://www.amsenergy.com/fuel-cost-calculator/
** https://www.nordicghp.com/wp-content/uploads/2021/10/001850S... (I selected the split-system here because it avoids the efficiency and temperature losses from a glycol-to-water plate heat exchanger that the monobloc units would entail. I need every degree of leaving water temperature that I can muster as I determined experimentally that my house is able to be comfortable down to 12º outside air temp at a boiler LWT of 130ºF on 1st and 2nd floor, but needed 145ºF in the attic [so would need to have the emitters [currently finned baseboard] replaced if I could only muster 120-125ºF LWT].) Spacepak is coming out with a split ASHP sometime soon, but has no technical literature published yet and I'm not going to be the first in the nation... :D
I studied the crap out of this, because I was hopeful that with $10K of incentives on the table that this could be close enough to make the switch worthwhile and eliminate on-site burning of fossil fuels in the house. It seems like we’re not there yet and there’s no guarantee that electricity will inflate at a pace slower than natural gas over the next 20 years, so this could get better or worse. Maybe the only supplier goes belly-up. Maybe something better comes along and no one wants to buy a house with this weirdo system in it. Parts would probably not be in stock at the nearest two supply houses. Only a few plumbers could work on it. In a scenario with that many unknowns, dropping in a $3K combi that everyone knows how to work on and parts are on the shelf 10 minutes away for $3-5K out of pocket (after factoring the almost $3K incentive on a high efficiency gas boiler) is a way better play and then see what comes along 10 years from now at the boiler mid-life or 20 years from now when it’s due for replacement.