I use Wrightsoft Right Suite Residential. I always follow the notion that the best money you can spend is on insulation. The purpose of the manual J at this stage is to correctly size the equipment. You were between a 4 and a 5 ton, leaning more towards a 4 ton, but I doubt that you would get it down to a single 3 ton unit. The percent increments become much larger once you get down in unit size. So yes, you will save more energy by putting in more efficient windows, but in terms of heatpump capacity, you would be pushing the envelope. In addition, you want some response time. Plus, we are doing all this over the internet, so this is just advise, you need to get someone local who correctly sizes your system and builds it efficiently.