I think most of us made the assumption that past a certain necessary level of glucose available to the brain, there would be little benefit to willpower.

A related example: creatine significantly increases timed-IQ-test performance on average in vegetarians, and not omnivores - creatine (and its precursors, for endogenous production) is found in beef, pork, and fish much more than in plants.

What I'd like to know is where I lie on the marginal improvement/dose curve at any moment (as you warn, an accurate model of this may be quite complicated). If it's hard for me to predict this, maybe I can titrate (not all proposed magic bullets are easy to incrementally dose and quick to reflect results, but some are).