Not a conclusive test because it was only quick testing, but on my drive back from Melbourne, I had just about the exact same fuel consumption using 91 RON, 95 RON, and E10. If you are are driving the car just for highway driving and not accelerating hard etc, then fuel consumption shouldn't really vary between the different fuels, which is understandable when you consider the purpose of the octane rating. I'm not sure about the statement of 91 being more efficient than 95, but any number of factors could be at play. Well apparently, all grades of fuels contain the same detergents that make it healthier for the engine. So whether it be 91 or 95, you should still get those benefits. From what I've heard, the only fuel with different types of additives to the rest is BP Ultimate. Just what I heard though.