Oh boy! I'll try and be brief. On any turbocharged Sube(since 02 model year) the sensors present to determine timing can take advantage of 100 octane(U.S. rating, so 104 or so in other parts of the world). Now, if Subaru finds it cheaper to adopt this "system"(hardware, software) or parts of, because of economy of scale etc. maybe there could be a difference in that the system on the XV could take advantage of higher octane. ClubCrosstrek getting peppier response and better mpg falls in line with benefits of higher octane especially living in a warmer climate like L.A. Summer time(82-98 degrees) I will top off my tank with some premium(93) in consideration that I will be blasting the A/C and pasting the throttle to the carpet often for more than a second or two. Keep in mind that if you her slight knocking on a consistent basis the odds of you having some crappy gas is high. With most modern cars(last 15 years at least) knock sensors will keep retarding the timing to control knock(detonation). That's why there are some people that say you don't need premium in a WRX, or STi. because the engine won't knock so they think they're fine. I know, stay focused, I'm trying. Higher octane won't hurt XV, driving in hot temps will see biggest benefit. Cold temps of negligible or zero benefit and could take one second longer to start. Last point I promise, it is common for gasoline manufacturers to add the most detergents to the premium fuel and(I'm cheating here) really cheap no-name fuel has minimal detergents.