In a residential application, my suggestion is turn off all items not wanted during an outage. Check to be sure the occupants will tollerate the items being off for 24 hours. During those 24 hours, place an ampprobe with a max function on the incomming feeders, and vwola, you get the exact surge capacity needed. The standby rating of the generator, could be determined by watching the meter for a half hour or so, and determine tha actual demand.
