I am a Commercial/Industrial Tech with 23 years experience in that field. I am considering putting in a Unico 4860 (410a TXV) air handler in my 1881 one-room-schoolhouse-turned-residence, but I am concerned about the choice of an outdoor unit (leaning towards a Lennox XP-Series heat pump), considering the 30+ degree delta T and supposed SEER-killing effects of the aforementioned HV system read elsewhere on this site. The supply ducting (SpacePak) and the return ducting are in place. Considering 20"-thick stone walls (and awesome insulation on the areas without stone walls), I'm sized for a 5-ton load. I was wondering if two-speed compressors can be used with HV systems. Seems appropriate that, at 80% capacity, I can cool and dehumidify with 48K btu in lower-load conditions (even with the fan at a constant speed) but I have no experience in the area. Any intelligent input would be appreciated!