We are replacing our old AC and electric furnace with a heat pump and an electric furnace with variable speed blower. The decision we are struggling with is single stage vs multiple stage heat pump.

Our house has two levels, and the upper level is always HOT in summer without AC. The ducting to the upper level should be bigger but we can't change it. Our winters in Eastern Washington can be very cold and long, so we are looking at the HSPF rating more than the SEER. We are trying to decide between two Rheem systems:

Single-stage Rheem RPQL-036JEZ heat pump 13.00 EER, 15.50 SEER, 10.00 HSPF

2-stage cooling/3-stage heating Rheem RPRL-036JEZ 12.75 EER, 16.50 SEER, 9.40 HSPF

We like the higher ratings of the single-stage unit, especially the 10.00 HSPF, but wonder what we'd be giving up by not getting the multiple stage unit. Do the benefits of multi-stage outweigh the lower HSPF and the additional $656?

Thank you for the help!