Allow me to shock U concerning some sizing realities in your climate toward controlling humidity.
I live in SW Wisconsin today 9/4/12 at 2-PM at Lancaster it was 90F & 54% RH; indoors it is 52% RH & 76F with good air circulation & totally comfortable.
Lancaster, WI very close to me, at 3-PM on the hour updates, it was 91-F; 50% RH; Heat Index: 97-F. NOW at 3:26 PM it's 50% RH in here on my first floor area & 76-F; around 25-C.
The indoor contains 45.7 gr/per/lb/air; outdoors 116 gr/per/lb/air; A/C
has to remove 45.7 gr//per/lb/air to get to 52% humidity level indoors.
This is a 1937 farm home loaded with 13 windows on 1st floor &, NO shade until very late in the afternoon; first floor area 620-sf have a
Half-Ton window shaker with an adjustable floor fan positioned to move air through all the rooms & back to the A/C.
Okay, 620-sf divided / by .5 (1/2-Ton)
is 1240-sf per/ton of cooling.
3000-sf / 1240-sf per/ton of cooling is 2.4-Ton;
Well,
U would have duct losses, etc., however, your home is way, way better insulated & protected from radiant & convection heat transfer than my home!
I have a Half-Ton on the 2nd floor which I only use in the evenings...
These small units have kept me perfectly comfortable in 112-F Heat Index.
How in the world could anyone 'initially' oversize equipment by that much?
Your home's calc should not be near where they had figuring it; even now it's still oversized for effectively controlling humidity plus meeting the sensible load.
I've never had a load calc performed on my home by me or anyone else; however, these light weight units do the job perfectly & use less wattage than most indoor blowers use!
It is amazing how much U can effectively cool with small tonnage; my all electric home monthly bills would shock your shoes off!