It does appear that modern Lexus vehicles don't benefit from higher RON fuels in terms of performance and MPG. Having said that, the benefits of them may be a long term thing, especially with the extra additives that are supposed to help clean the debris out.
It is worth remembering that the US and UK cars are exactly the same in terms of engine and power produced. Therefore these cars are meant to run on Premium US unleaded which is 91 Octane, the equivalent of 95 octane in the UK.