Terry,
When you said:

"One thing to watch out for if you stay in emergency-heat mode for a
long time. Snow and ice can build up on the outside unit. ";

I took that to mean you thought the frost would build on the outdoor
unit with the thermostat was set to emergency heat. Seems you ment
something else.

The HSPF is the number you look for as far as heat output including
defrost cycles. You want the region III HSPF. In my area, we use the
region IV HSPF due to our higher average temperatures. If the HSPF was
3.4, that would be the same efficiency as heat strips. HSPF is BTUs
per watt. Most heat pumps, even the builder grades will produce a HSPF
of 6.8 or higher in my area. In your area it will be a bit lower.

The COPs do not include a deduct for the cost of defrost, but according
to the manufacturers I have talked to, you are better off letting the
heat pump run, even down to -20 degrees outdoors.

Around here we set defrost to between 60 and 90 minutes per cycle.
Most defrost systems will terminate after 10 to 11 minutes even if the
OD coil is not completely clear.

Of course, if you are only paying 3.5 cents per kwh, who cares about
efficiency. If electricity is free or very cheap, it is hard to
justify high efficiency. we pay 6 to 8.5 cents per KWH around here, so
that changes the equation. I have talked to people paying around 17
cents per kwh! OUCH!!

Stretch