Have a new 2011 RX350 with 5000 km. On a 5 hour highway trip, checked fuel ecconomy one way with 91 octane and return trip with 89. I used .6 litres more per 100 km with mid grade so, on a cost basis, no advantage - 91 octane is about $.06 more per litre than 89. Will check again on next road trip using 87 octane but seems like using high test does not cost any more per km (or mile) driven. One interesting thing is there is one gas station that sells a 94 octane. Sticker on inside of fuel lid says premium grade rather than specify an octane rating. I'll try a tank of that on a future trip.