Ours is a 2 ton for a little over 1700 square feet. I did the manual J twice, because I thought I had got it wrong, calculated for 76 inside and 110 outside, and it seems to work just fine.
But when we moved in we had thin plywood panels rather than drywall so I tore everything out, added another row of 2x4's which allowed a thickness of 9 - 10" of fiberglass bat in the walls, about R-30. And along with low E-windows and doors, powered attic fans etc, you get the idea, it's well insulated