I have always used 87 octane in my 2015 RX . I get around 20 to 20.5 in town and 22.5 to 23 on highway trips. I have tried 91 octane before but noticed little if any difference and can't justify the cost difference, I think my RX runs great. Hope that it last a long time because I will absolutely look for something else before i own a 4cy Turbo in something this size. I quite familiar with turbos, repair cost, extra maintenance (having to change sparkplugs every 40,000 miles) also oil gets dirty alot sooner. Just not for me.

^^ Same here. No four-banger turbo engines with CVT transmissions for me. I hope I can keep my wife's 2015 RX350 and my 2013 Subaru Outback 3.6R running properly for a long, long time.

CVTs are another story. I have a semi truck driving friend that tells me I wouldn't believe how many rebuilt CVTs he delivers to Nissan and also picks up the dead ones.

I have a 2011 RX 450H (hybrid) with 224,000 miles. Several years ago, I stopped using premium or mid-grade, and started using just regular gas. I do not hear any pinging and do not notice any difference in performance. I am getting about 22 mpg on the highway at 75-85 mph with a fully loaded car (two adults, back seat and cargo area full of heavy stuff). This may or may not be less than what I used to get on premium--I don't remember what I got back then.