Find a
BSFC chart for your engine (none posted yet), and look for the RPM band that gives you the least fuel consumption at max load. This is usually 2000-3000 RPM, but varies based on engine design. If you have a vacuum gauge, keep it at 2-5 in. Hg, almost floored but not into the acceleration enrichment.
Better yet, get a scangauge or mpguino! Then you'll see for yourself.