That's an age old question for sure. Most of us size for the peak, not the bottom. I added a tachometer to my EU2200i and based on the RPM's as well as "listening" to the load (scientific huh?), I'd say the sweet spot for minimal fuel usage is around 25% load. Obviously running it with a less load will take gas no matter what, but I have no good way to measure that difference. Some manufacturers actually list those specs on gas usage.I would be curious what the fuel consumption would look like on one of the larger units - like the Honda EU7000 or Powerhorse 7500 - at light loads. There is a threshold of power generation before the engine needs to make more power.