thing is that 5s-fe usually does not get better MPG from 93 fuels ... perhaps the difference is roads, driving style, load, weather/temperature, city vs hwy combination, traffic patterns, poorer quality of 87 fuel?
5s-fe is built to run most optimal on 87 fuel.
however 1mz-fe runs much stronger on 93 vs 87, as 87 actually impairs it factory performance specs (not sure about MPG though).
wife's 5s-fe @ 80k miles usually gets 28 MPG on 87 (last checked on Winter formula), but I am no easy on it when driving