I think my manual suggests 89 under certain circumstances such as maybe towing.
As to high octane deposits, we no longer use lead. I had a 68 Mustang 302 Hi-Performance. At about 3000 miles the performance would start falling off. If you did not change them by 5000 miles it would start to miss. Typical high test fuels in that day were 98 or higher octane. Clark brand was 100+ and there were higher octane readily available. All that lead would start to short out insulator.
Alcohol will get less MPG, but properly tuned the engine should also put out higher power. I did not know you could buy pure gasoline anymore. Alcohol is also used to raise octane as well as lower emissions. What compounding is done to raise octane above 87 might have a number of solutions. At one time it was claimed it started at the distillation process resulting in a more pure product. But an easy solution would also be to add more propane. More propane is also mixed for winter gasoline to make starting easier because it vaporizes easily at low temperatures. 40 years ago, farm tractors often had a propane option. The down side was in the handling and less horsepower. Propane delivery companies usually ran their trucks with propane and in a day when everyone changed oil at 3000 miles, they ran much farther. Oil with 6000 miles looked like it just came from container. Far less polutants using propane, less maintenance, and far cheaper fuel because it had no road taxes.
87 octane also burns faster than higher octanes and part of the reason you can get spark knock. Also power tools, lawn mowers, etc. will stress using 87 only. In those lower compression engines the faster burn provides easier starting.
To sum up, higher octane fuel in your Malibu might have slightly less mileage but might also add to engine life because of the gentler burn and slightly less polutant making it to the oil. Higher compression adds to the efficiency but if your engine is being retarded because of knock it will lower efficiency. Knock is always bad.
But with the latest generation of engines, direct injection, everything might change. Part of how they improve efficiency is to raise compression substantially. I saw where one of these claimed the compression was over 11. With fuel directly injected and carefully controlled rate they seem to have overcome an old pollution concern. To lower NOX emissions, compressions often dropped below 9 and the EGR gas was necessary to slow the burn. If the computer is able to automatically adjust you should get better mileage and power from high octane in one of these newer direct injection.
And they seem to have slightly less power. Especially noted on 20hp lawn mower, but then it might be only a perception since it also seems to run quieter.
