Also vary a bit between winter a summer, basically in winter they can get away with putting a bit more volatile compounds coz it's colder
Which, every modern ECU will do automatically based on output from the knock sensors.
In theory, your average Camry running on 87 is pulling spark timing to ride the edge of knock for best fuel efficiency by being lean, but how much? It was designed to be safe on even kinda shitty gas, that has lower than 87 octane at points, and the ECU is going to err on the side of caution.
That naturally aspirated 2AR-FE in a Camry does not have the ability to compress harder, so if you put 93 in it, it may only be able to "utilize" the extra knock resistance up to say 89 by advancing spark timing.
Meanwhile your average Golf TSI probably can, and the VW GTI I have demonstrably gets better gas mileage on 93 octane, even though it is "rated" for 87 octane (and therefore has a lower mpg claim than it is capable of), but this was an engine that previously was rated at 91 octane and nerfs itself so hard on 87 that it is dramatically easier to stall, and the power figures are rated on 91 octane anyway.
You are almost certainly spending more money on gas even if you eke out a percentage point or two extra mpg on higher octane fuels, as they are priced at higher margins and have lower scale.