Lots of good thought provoking discussion. I guess if I had more confidence that roll down distances had a direct one-for-one correlation to fuel economy, then I'd also try the experiment again. But I'd use a slightly different methodology and try to keep everything at operating temperature. After all, that is where the real results are achieved anyway. But the bottom line on the theory part is that I have yet to see a theoretical development which traces the relationship back to Maxwell's equations(That's a standard Electrical Engineering joke)
Certainly there is a promounced plateau effect. I have seen this in fuel economy testing in an Echo, under very tightly controlled distances. In that case, there was insignificant improvement above 50 psi. But I think the Insight may well be a different animal. Special LRR tires, special low loss hubs, special lubricants, well very light weight at least, and any number of differences. I'm willing to conceed that nothing above 60psi makes much difference, but I think the Insight is a different animal.