You need 13-15kw just to start a 5-ton AC unit. 4000 sqft house with high humidity 90 deg summer days (so anywhere in the SE US) will need at least 8-tons of A

You need 13-15kw just to start a 5-ton AC unit. 4000 sqft house with high humidity 90 deg summer days (so anywhere in the SE US) will need at least 8-tons of AC, so 2 units, and that's ~24kw right there if you need to cool the whole house. But the more common practice is to run just one of your two units and then have plenty of room to run all the small wattage things in the house without needing to actively budget power. Having lived through more than a few week+ outages in Jul/Aug/Sept heat (including 3, 6, and 8 week outages), I certainly see the value if you can afford it. Comfortable, but not necessarily extravagant. ETA: We also learned our lesson relying on NG and converted to dual fuel with a 2-week supply of propane.