I've compared Shell 98 RON with 95 RON in the firms Pan Euro's, (because it doesn't cost me anything) and you don't notice any difference in performance. However, I'm sure they put additives in to justify the extra price.
The RT has probably got a higher comp ratio to gain the extra 10 bhp and so will gain from the higher octane rating.
The 40 plus age group among us will remember when you could buy 2,3,4 and 5 star petrol.