This house was a neat project I got to hand pick the equipment for. It was a 3100sqft home with two 3 ton 10 seer trane units. The duct in the attic consisted of 3 9" flex supplies to spider boxes. One unit had shorter 14" return. One longer 16". Needlessto say both had mold issues and lost capacity. The old units pull 13amps. New units 7-8.
We installed two more supplies and a return into a sunroom which added another 380sq ft to make it roughly 3500.
We used two 2.5 ton identical units which fit the existing undersized duct better. (Sunroom unit running lower static now) Both units have 22kbtu compressors. The other unit is still running at 0.70 - .75 TESP but in range on blower chart @950cfm.
The house has been doing great. They keep it at 72/74 during the day and crank the bedroom/sunroom unit to 69 at night.
Customer went from roughly 375/month to 275-290/month.