tedkidd, thanks for the comment (and thanks to all others), the home is 1995 and was told when we bought it 2 years ago it was super well built. (other than the poorly designed duct work i guess, i am working on this--other post). The attic is well insulated, but can't verify the cathedral ceiling, or if they put insulation over the 10+ can lights. Or verify the wall insulation. Really no air leaks or other obvious problems. Can't imagine an easy way to improve it.
There are 2 heat load zones for this unit--2500sq ft total, 500 sq ft is cathedral ceiling 14 foot high, other ceilings are perhaps 10 foot. 135 sq ft of west/south windows. I have tried lowering the blinds, and it makes a DRAMATIC difference in how hot the room gets/previous unit worked.
What do you think? Take a small chance and go for the 4 ton? Or take a risk of high humidity?