Simple well explained answer. High octane for High compression engines to delay ignition. New vehicles have "Knock Sensors" which hear the ping and adjust engine to compensate. In winter here in Edmonton (Canada) I always run regular. no ping no knock.. in the heat of summer with boat in tow and kids in car, I will throw in the premium as I have hears an occasional ping under HEAVY stress.. up hill, towing and hot...
Premium is not a "better" fuel.. its octane rating.. do I notice a difference in mileage? over a 5 hour hwy drive one way on premium and other on reg.. not really.. and we are flat roads here..
I would think more important to use a "NameBrand" fuel vs a FasGas etc who buy end of the line fuels from the major producers..
If manual says "Recommended" vs "Required".. you can read between the lines. Call INfinity and ask if regular will void your warranty..
Mid grade not worth the difference.. but .10 per litter on 100 liters is 10.00 and I use about 100 per week x 52 is about 520.00 per year.. buys gas for the boat!
