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The single most critical load indicator is manifold vacuum, or in the case of MAP which is atmospheric pressure minus manifold vacuum.
This can change considerably at most throttle positions depending on the speed, gear, and grade the vehicle is negotiating.
If you are at the lowest possible manifold vacuum reading without full load enrichment, you are in the best position as far as BSFC is concerned, as long as you are in the proper (read fairly low) RPM range.
Once you get the feel for this load range, then you have to calculate which gear will be best for acceleration to your peak speed.
As a general rule the highest practical gear is usually the best selection. The exception will be when you are climbing a grade and need to use a lower gear to maintain a speed up the grade. In every case you want to avoid absolute WOT and fuel enrichment, unless it is necessary for avoiding an accident.
Install a vacuum gauge temporarily and learn the best throttle positions to maintain your vacuum around 2 inches of less without WOT. After a while it will become second nature and you could remove the gauge.
regards
Mech
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