Here's what I would like to discuss.
As you can see in this example BSFC map, the 25% load has a very tight vertical curve to it. So the sweet spot is much narrower then the 50% and 100% load lines.
Just moving up or down in rpm a little can take you away from the sweet spot.
At 2800 rpm you have the most efficient BSFC number of 0.70 lbs/hr.
At 2000 rpm you have 1.0 lbs/hr.
At 4000 rpm around 0.95 lbs/hr.
Food for thought???