you are confusing matters by assigning definitions that are wrong - assuming you are referring to the UK, super unleaded has to be at least 97 RON. Fuel sold as premium unleaded is bog standard unleaded at 95 RON. Some branded premium fuels such as Tesco Momentum claim 99 RON. Shell V Power claims to be 4% superior fuel but does not claim a particular RON. It has dynaflex whatever the fuck that might be. Note, these premium fuels do not claim to be super unleaded as I guess they do not want to be associated with the 97 RON super stuff sold by Sainsbury's.
Anyway, keep buying the posh petrol. It's not likely to be any better for the GS but it will make you feel better and redistribute more of your money to HMRC.