Sorry, you're right, I meant to say top speed not cruising speed. Although cruising speed is relevant too - at your ideal cruising speed, your car is most economical, quietist and smoothest.
My statements are based on the fact that the average New Zealand driver is terribly uneconomical, has no idea how a good car is driven, and has marginal - at best - driving skills. You obviously care about driving, and the performance of your cars, and you're a bit pedantic, so I can make an educated guess that you're probably a better than average driver (even if you are a Honda fan ).
However, you have to agree that the way the average driver drives, there's no way they would notice the difference between 91 and 98 octane fuel - they probably have 3 soft tires, unaligned wheels and completely screwed gears, and drive only in straight lines, even around corners. They also probably haven't driven a car at top performance, so have nothing to compare their car to.