It's my experience that the vehicle is already "tuned for it." There is no where level where I live, no where. It's all either an up or a down while turning. Experiments with both octane and octane enhancing fuel mixes has provided me with optimum performance and optimum fuel mileages over the course of several newer vehicles.Higher octane fuel won't make a difference. You'll get more power but only of the car is tuned for it.
I've also tuned and datalogged every mile of a variety of stock and extensively modified Subarus and am intimately familiar with real world, data backed, engine performance in this environment. I'm not guessing.
I also don't give a floating feather's energy to worry about pennies. I want the best on hand 100% of the time even if it's not used. So far I exceed estimates on all estimable parameters.
Others? Y'all, do youse.