There was a small amount of controversay back in 2003 when I was picking your most talented brains for information to help me design my new house, and I had said I would give a followup after the system had been in operation for a while.
House: 4000sqft (2800sqft in a two story section, and two 1-story sections adding up the other 1200sqft), slab foundation, NW Arkansas (south of Branson, MO)
System installed: 3.5T 14SEER (13 SEER plus TXV) Tappan heat pump with VS air handler. Arzel 4-zone system. Duct work is oversized, so that each zone can take the airflow.
System is working pretty well, except the airflow is really a bit much for the smallest zone (noisy flow, and we had a Bernoulli effect issue in the family room bathroom, definitely not a room you want the supply system sucking rather than blowing). But overall pretty good.
Winter: 3.5T HP handles temperatures down to about 25F without auxilary. Even down to 7F, the auxilary heat doesn't fire all that much.
Summer: 3.5T is too much capacity for a 92F outside temperature, on this zoned and well insulated house. The system does not run long enough to do a really good job dehumidifying. My father-in-law across the street has a 10SEER Tappan, and it does a great job dehumidifying.
I have an all electric house, with two 50gal 95% electric water heaters. The electric bills, for this 4000sqft all-electric house, along with my home office, run $200/month on bill averaging.
The home office: I have considerable amount of energy consuming equipment, so I have an 11SEER supplemental AC unit handling the heat load of this room. The low speed VS fan sweeps the rest of the house nicely, but it's not sufficient flow to sweep the heat production in my office.
I used Don's wonderful HVAC-Calc program to generate my stab at the calculations for the hosue, then used that data to shop for an HVAC professional to do the final design and installation. Was amazing the people who disputed my calculations and insisted the house needed at least 5T. One guy insisted the house needed 5T downstairs and 2.5T upstairs. If I had to do it all over again, I would have pushed harder for the system to be downsized to a 3T, or I would have tried to hold off for the few additional months necessary to get a Copeland UltraTech scroll.
Thanks again for all your wonderful advice and inspiration!