I had 4 contractors bid on my central air full install. 3 suggest 4 ton unit. One says a 3 ton will do. The one who suggested a 3 ton measured every room - he took his time. The other guys measured just the perimeter of the house. 3 ton guy estimated living space at 1600 sq feet, where is the rest of them estimated it to be 2000. I am located in north jersey, 50 year old cape, 7 feet ceilings upstairs, many high trees around, original windows and insulation. Do I go with a 3 or 4 ton or should I go with 3.5?