Really good thread...I can only throw out a few thoughts right now:
The Power Running guy makes the points:
1-be a s strong as possible
2-Do some intervals
3-run your race pace fast
4-substrate utilization/depletion is the limiting factor in endurance performance, not O2 consumption/utilization.
Many studies of late have shown that neither myoglobin or hemoglobin are depleted in O2 to a degree that will limit performance, even at extreme workloads.
Ideally one is "very" fat adapted such that, at any given output, one uses more fat and less glucose for activity. As intensity of exercise increases more and more carbs are inevitably used which can cause substrate depletion...also there is the issue of pH change with increasing workloads.
"Survival will be neither to the strongest of the species, nor to the most intelligent, but to those most adaptable to change."