One other factor is weed control. I feel I get better weed control with the narrower rows.  This is especially true on our lighter soils.  I am not satisfied with my drill.  I get erratic spacing.  You can find gaps big enough to walk around in.  My depth control is terrible.  Residue causes problems.  No-tilling is nearly impossible.  But on our lighter soils 7 1/2-8" rows consistently out yields wider ones.

Something I find interesting is a statement on Beck's PFR results last year

Each row spacing has produced the highest
yield in a given year. The only correlation we
have found that relates to which row spacing
does the best in a given year is heat. More
specifically, the month that has the most days
above 90 degrees has determined which row
spacing produced the most in that year. When
June had the highest number of days above 90
degrees, 7.5” rows produced the most, July, 15”
rows, and August, 30” rows came to the top.
This pattern occurred in all but three of the past
twelve years.

This is a fascinating observation. Is it fact or coincidence?   I haven't a clue but it can explain a lot of the variation in results when comparing row width.  We try to remove as many variables as possible when conducting tests, but we need to keep our eyes open for things we can't control.

edit: typo's fixed ...  I hope