Some anecdotal evidence on the effect of tire pressure:
We have a camper-van that we use for vacations. I purchased new tires for it and for some insane reason, they pumped up the tires the the maximum pressure on the sidewall. I should have checked the pressures myself, but I was in a hurry to get going. It drove just fine around town, but it became terrifying in a crosswind on the highway. Once I set the pressure to the correct values per the manufacturer's recommendations, the cross-wind problem went away. Now I know this is a full size van and not a Leaf, but it was a lesson to me. If the higher tire pressures result in any loss of performance (stability or breaking), its not worth, at least to me, the extra advantage that would be gained in efficiency.