I haven't performed any scientific tests, but I usually see about 2-3 mpg better economy in my 07 Civic EX. As far as I know it has a knock sensor, and subjectively, the car feels spunkier off the line and doesn't run out of breath as soon when downshifting to pass someone on a 2-lane highway.
Run the numbers and see if it's worth it. I calculated the following figures that justifiy the extra cash up front:
Regular gas (here in Olympia ~4.25) @ 35 mpg highway = (4.25/35) $0.121
Premium gas (~4.45) @ 38 mpg highway = (4.45/38) $0.117
Therefore this equals less dollars per mpg. Even at only 2 better mpg the extra cost would be worth the mileage. One may spend more at the pump at one time, but one also visits the gas station less often. The effect is also amplified the worse the gas mileage gets. If with regular you get 15 mpg, then assuming premium is 20 cents more expensive, you only need an improvement of 1.26 mpg to equal the additional cost of premium.
Don't you love maths?
