At your yield levels I would think you have some room to up your population whatever row spacing you use. We did a number of years of side by side population studies in 30" rows and found we were not planting thick enough. I would suggest you take some time and do some strip trials. Don't go strictly by one year though, do several years.

All my side by side observations were at exactly the same population. I did not want to skew the results by inducing two variables into the test at one time. Doing that, a person does not really know if the yield increase came from the narrow row or the population increase. If a person can push populations higher BECAUSE of narrow rows, that benefit would be in addition to what response we got FROM narrow rows over wide.

John