Hi Jerry C - It's hard to give up those old habits isn't it. I have used HVAC-Calc for years and have previously done Manual J calcs by hand. Either way, by hand or by HVAC-Calc, you come up with the same answer, at least you do after you fix all the mistakes you make doing them by hand.
I did a load calc using Manual J and again using HVAC-Calc on my own house. I came up with a load of 29,000 BTUH (total cooling). This was with "no inside shading" and "no outside shading" and with the design temp as it is built in to the program. I have a 2 1/2 ton unit (existing when I bought the house). We have what I call "Perfect Air Conditioning" - we just forget about it - we are comfortable. Yes, on a hot sunny day the unit runs what seems like all afternoon, actually it does cycle a bit, but not much. That is exactly what it is supposed to do.
For my own customers, I have added 5 degrees to the outside design temp that was built in to the program. Summers seem to be getting hotter and not all customers will just set the tstat at 75 and leave it alone. I do explain to them the pitfalls of oversizing with the sales call. This often helps get me the job! I have done a load calc and I have shown how the 600 sq ft per ton folks can't possibly be right and can't possibly care about their true comfort level. Occasionally I have run into a customer who really feels they must have a larger unit. I give it to them. And with their agreement, we write "AC sized by customer" on the contract.
Works for me Jerry, I think you have bought the best program available with the best support.