I am in the process of evaluating proposals from builders for a house we want to build near Pinehurst, NC. The house is a 2,400 sq ft one level home, over a 2,000 sq ft unfinished basement. The heat pumps that they are quoting are Lennox 13 SEER models. Would it be better to consider a two stage HP like the Lennox HPX16? How much more expensive are they to install? Do they keep the house more comfortable? Any help would be appreciated.