I'm observing two ranges of fuel consumption. When travelling at 55-65 I see something like 24-26 mpg. In my parts I-80 has some significant stretches where speed limits are 80 mph. When travelling along that way I see something like 20-21 mpg. So long as you use the minimum octane rating, 87, you'll likely see these numbers. Higher octane does not improve mpg as octane rating has nothing to do with energy content. If you're travelling on a hot summer day with a heavy load (eg on the turbos alot) going up in octane might be a good idea to ensure good margin from cylinder detonation. Otherwise use the specified 87.