Steve, the yield potential PER PLANT is the same.  Herman did it with a population of 33,000 harvested ears when most people in Illinois were probably harvesting 20,000.  The breeding programs have now selected hybrids which are capable of standing at 40,000 or more, if they have the fertility and water to support doing so.  (BTW, Herman was in a hurry to harvest that field in 1975, in the rest of that article he says that lodging was imminent-he was pushing those stalks to the limit.)

Monsanto has a goal of doubling the national corn yield by 2030, or something to that effect.  Something really drastic is going to have to change basic agronomy for that to happen without the majority of acres being irrigated, or using typical university recs for soil fertility.  (Or who knows what fertilizer limits EPA will be trying to impose by then.)  I'll submit that one of the few game-changers which could possibly make the next big leap would be corn that can nodulate it's own nitrogen.  Otherwise, there is somewhat of a limit to what the synergy of sun-H2O-N-P-K can produce in harvestable dry matter per acre and Herman was getting pretty damned close to it 4 decades ago.  BTW, I read through the list of 2013 NCGA contest winners and none of them harvested with a 750 Massey....