Fuel economy may or may not be different. For aggressive stop and go driving fuel economy may suffer because of spark retard. On a long freeway cruise it may not be noticeable.

You bring up an interesting point about fuel prices. The price difference between regular and premium seems to be about 20 cents regardless of price. Back when it was a buck a gallon premium fuel was 20 percent more expensive. Now, at two bucks a gallon, premium is only 10 percent more expensive.

Duke