I remember reading a review by Porsche years ago on high quality fuels v ordinary stuff. They reckoned there would be no difference in performance because the on-board computers would analyse the burn and adjust all settings as required. They firmly believed that there was no performance advantage to be gained.
After all, it comes out of the same hole in the ground, it's just the additives that make the difference.
The engine management system will adjust to whatever fuel is supplied...but 98 gives higher output so should give better performance.
Have to correct the second statement: It does not come out of the same hole in the ground. Crude oil and gas is formed from dead sea creatures, underground and under intense pressure and temperature (coal is formed from dead plants). Crude oils that come from different parts of the world differ in both density and sulphur (and a host of other less important qualities). A quote:
"The variety of oils sometime seems as variable as the minds of man. Each source rock is unique and can vary geographically as well as geologically across it's extent. The kerogen (pre-oil) contained within these rocks have a chemistry determined by the origin of the organics originally buried millennia ago. A second influence is the chemical makeup of the rock.
One of the main differences is sweet and sour crude. Sour crude usually originates in a carbonate prone source which contributes the materials, usually sulphur, necessary for H2S or other compounds found in sour crude.
Another is the 'weight' of the hydrocarbon. It varies from a near pure methane gas to a bitumen thicker than the tar used to build roads. Much of this is caused by the orininal organic composition but further complicated by the heat and time acting on that material.
The higher prices go to lighter oils mostly found in the North Sea, Africa and the Gulf of Mexico. The Canadian oil sands are much thicker and therefore less valuable all the way around - higher production, transportation and refining costs."
If you then add into the mix the type of refinery used to process the crude oil (with/without reformers, cat-crackers, hydro-crackers, thermal crackers, isomers, with/without chemical plants etc) then the petrol produced can vary enormously...even within the constraints of high EU specifications.
Add to that the proprietary additives and you finally get the petrol you want...or not!