My previous European car ran cooler and had more power on the highest octane, which is still lower than the normal fuel in Europe. Basically it refused to run on anything less.
My current car a Falcon will run happily on anything, I’m sure that if I put kero in it, it would not complain too much. It also is fitted with gas.
As to the cruise control I have used cruise control for about 20 years and I have always found it to be more economical on all my cars. I use it full time city and country
I did hire a Camry at one stage and the motor obviously was not powerful enough to handle the cruise control so the revs went up and down while it tried to handle the set speed. It was so annoying in hilly areas that I turned it off
So as with everything do your own research and work out what is best for your car and your type of driving
