Looking at Luxaire, Rheem, and Bryant. In very southern Arizona where we have significant heating needs in the winter (single digit temperatures) and cooling needs in the summer (over 100!). Unit needs to cover about 1800 sq. ft. Wondering about how efficient to go; up to 97% AFLUE furnace and 16 seer AC. Will there be an appreciable difference going this efficient, or can I back off in a way that makes sense?