With only a .5MPG improvement, it's more expensive to run mid-grade.
As far as increased power from simply adding higher octane fuel, that for the most part is a myth. There are actually a few cases where that can decrease engine power. Your best bet is to just run the 87 octane that the engine was designed to run on.
As far as increased power from simply adding higher octane fuel, that for the most part is a myth. There are actually a few cases where that can decrease engine power. Your best bet is to just run the 87 octane that the engine was designed to run on.