Mr Allen--Lowering your load is the best way to save money per month and be more comfortable. If you are building, why don't you consider structural insulated panels? I helped a couple design a 4500 sq. ft home with only 2.3 ton load! Our firm guaranteed average heating and cooling costs at only $48.00 per month in Virginia with heat pumps. The couple also said it was the most comfortable home they had ever been in. The real key on comfort is both the house and the HVAC equipment!
In virgina i find homes that have 2 ton units that in Texas would have a 4 ton