Your logic is not correct
If you buy standard 95 Ron. (Unleaded) it meets the International standard, no matter whether you buy it from, Shell or Tesco.
Now Shell claim to add cleaning detergents to make theirs better, but it does not alter the RON rating, it will not perform better …. It ‘may’ keep system clean, but could also just be marketing smoke & mirrors.
Now for Super Unleaded (97-99 RON) you say you believe that will be the same on all forecourts …. why do you believe 95 Ron standard is not the same yet 97-99 standard is …. That is the flawed logic.
All super unleaded meets the appropriate standard for 97-99 RON … one super special name may sell it to 99 RON another only to 98 RON
Should I use it …. Super Unleaded has an ignition suppressor that prevents pre-ignition (engine knock) when under high compression.
Unless your engine is a high performance, high compression engine it will not make any difference to performance …. It won’t harm the engine, but you are just wasting money.
I find it amusing on US boat sites, guys use Super Unleaded all the time, and use SeaFoam additive on every tank, it makes zero difference ! …
As to why I fill my tank when winterising …. Air space = condensation, so filling it reduces condensation.
I have a full service
before I winterise … so engine sits in clean oil, filters when idle.
Why leave engine sitting in old oil for 6 months ? … that though is my choice.
When I start season, I run fuel as low as I can on fuel, before topping up, so that I burn off all old fuel first.
I use Shell 95 Ron as a Shell garage is 1/2 mike from my house, but be happy to use (and have done when on offer) Sainsbury’s fuel, as that is on my route to launch site.
As per my original post, when UK governments changes to force increase of Ethanol, I may then need to start using Super Unleaded… but to avoid Ethanol, not to get better fuel.
Take a read:
https://www.regit.cars/car-news/is-supe ... -car_65626https://www.which.co.uk/news/2020/09/su ... d-to-know/
FourWinns H210, Volvo 280-C-N duoprop, Monster MTK tower, SBS 2600 twin axle trailer
Tow Vehicle - Landrover Discovery Sport