Bob, I've pondered the same question, here is what I have:
The graph shows mixture sweeps at 2000 to 2400 RPM. DA about 10,000 ft., dead stock setup. I was interested in efficiency...nmpg, so I plotted the isopleths for reference. If you don't care about airspeed, the highest efficiency is at low RPM. Keeping in mind that fuel flow isn't quite the same as power - air fuel ratio may be changing too - the graph also shows that on the rich end of the spectra, speed is increasing with RPM, constant fuel flow. It doesn't hold up though as mixture is leaned. At the very lean end there is a suggestion that speed increases as RPM declines.