You will gain a huge amount of efficiency if you pair your genset with an inverter
which is capable of adding inverter
power to cover short-term start-up loads. Victron inverter/chargers do this, and I believe Mastervolt and some others will, too.
Then you can ignore the startup loads and size the generator so that it is running decently loaded -- as diesel
engines like to be -- at your actual sustained loads. I think diesel
generators are usually running with reasonable efficiency and low risk of bore glazing at 30% of their rated capacity. The greater the load as a percentage of rated capacity, the more efficient the genset will run in terms of diesel fuel
consumed per unit of power delivered. On the other hand, you don't want them running at or near their rated capacity for a long time -- accelerates wear. So the "sweet spot", as you say, would be probably 70% to 80% of rated capacity, as the maximum sustained load you would expect to encounter.
The beauty of the Victron and other modern inverter/chargers is that you can set the maximum power draw from any AC power source. So you can positively prevent the genset from being overloaded by setting the maximum power draw to, say, 90% of the rated capacity. When this is reached, the inverter/charger will start cutting back the charger
. When that fails to prevent an overload, the inverter will start pulling power out of the batteries
to make up the shortfall.
This totallly solves the inrush current
problem with air conditioning
-- very cool.