We analyzed gasoline samples by GC/MS. We identified and quantified each and every peak in the chromatagrams. Xylenes are indeed present, more so in higher octane fuels. There was also toluene and trace amounts of benzene.
By trace I mean near baseline.
Higher octane does burn slower in a more controlled manner. It has more high molecular weight hydrocarbons in addition to aromatics.
Don't believe me? Put a match to n-pentane and compare that to n-decane
I work in oil refining. In the last 20 years refiners have invested billions of dollars into equipment to remove BTX. Is there some still present? Yes, but at very minimal levels. The days of jacking up aromatic(BTX) levels to increase octane is long gone and the EPA mandates this.
Higher octane fuels do not burn slower.... in fact if they did it would lower their octane rating. Detonation takes heat and time to manifest itself. Anything you do to slow down combustion increase the risk of Detonation.
Putting a match into a hydrocarbon doesn't prove anything. Detonation isn't normal combustion, it's abnormal combustion.
And yes I have taken both organic and inorganic chemistry in HS and college. You are talking about theory and I am telling you that in practice premium and 87 have the same energy content depending on the time you take the sample. The thing you must consider is there is no recipe or formula for gasoline. It's a chemical soup of a variety of components that are constantly blended to hit a performance specification. Some refinery streams are poor quality and some are high quality, but at the end of the day they all will be blended and nothing is wasted.