You bought a Lexus and want to skimp on the gas for it?
It’s 3.5L v-6 with a 10.8:1 compression ratio. Even oin their website, Lexus tells you to use 91 octane fuel
Ratings achieved using the required premium unleaded gasoline with an octane rating of 91 or higher. [i]If premium fuel is not used, performance will decrease.[/i]