I dont really want to rain on all the theory, but petrol blends vary a lot around the country to account for climate.
In fact they also vary during the year.
Petrol in hotter areas is adjusted to not dissappera as fast , in cold areas so that stuff doesnt freeze out of it.It probably varies between deliveries as long as it fulfils certain specifications.
Petrol companies have been known to use each others supplies when they need to.
This variation between shipments goes a long way to explain why some people swear by one brand and claim the only time they filled up with the other it was crap. Its possibly just a local effect.
I strongly believe all petrol companies blend feed stocks to set combustion and physical characteristics. A company to claim it is "higher refined" is a PR term and really doesnt exist in chemistry. Higher refined sort of means that it has been separated into more fractions (boiling point ranges). Whch you would then blend back to get the characteristics you want.
Petrol companies spend a huge amount of money convincing you that their essentially identical products arent.
iso Octane the aliphatic compound which is given as the 100 octane standard boils at about 125 deg (not the perfect measure of volatiliy but it will do)
benzene hasa RON of 101 (yah would have to add a lot to get 92 RON petrol to get it up) and a boiling point of 80.1 deg so yes it is more volatile.
Using toluene would be much better .. 114 RON bp and BP of 110
(in fact i used to add it to a nasty car i had way back when)
However both chemicals are more valuable as chemicals in their own right so i reckon yah wouldnt waste them to burn.
They are also rather carcinogenic etc .. so putting them in petrol would be a no no.
However the theory of aromatics leaving petrol blends faster has legs (well they are called aromatics because they evaporate easy (you can smell them ie they are aroma tic)
But i really dont know if the effect would be noticeable over a week. But who knows.
I wouldnt trust my nose i would only trust a gas chromatograph.
Of course the other thing is the other additives they add in .. petrols aint just petrols, which may have more effect than the hydrocarbon blend.
I reckon its what ever rocks your boat ... buy one brand from one servo .. and get your car tuned to that if the extra 1 hp is worth the trouble. Dont buy from non branded servos' and if you get a "bad" lot of petrol dont go back as the owner is pulling shifty tricks. Buy some toluene and add a bit if you want.
guess what i did in a previous career