Well, initially we were talking about <1400 rpm. And yes, prolonged operating at that engine speed will produce more soot, more egr, shortened dpf life, and shortened turbo life. In Nicole's example of a 40 hp load, the engine is more efficient at 2200 rpm than 1450 rpm. I'm struck by how ugly the contours below 2500 rpm are compared to above 2500.
The example was not of a 40 hp load, the example was of applying proper ratios to reading the chart.
The example you gave of 1500 rpm @ 12 bar mep is indeed a 40 hp load for that engine(cjaa I believe). And at that load 2200 rpm is in fact more efficient than 1450 rpm- barely. But the engine is a heck of a lot happier at 2200.
You're a smart fellow, but you're incorrigible. You're focusing on the wrong details. The example was a ridiculous one simply to illustrate the ratio.
Soot is only there when excessive fuel is dumped in for the air in the cylinder, and that'd only happen if you were trying to accelerate.
Or if you try to maintain speed going up a grade, into a headwind etc. I like to use a gear that allows for good fe and allows for decent acceleration without the need to downshift.