Some thoughts on this:
1) Higher octane (premium fuel) does not translate to more power. It's advantage is that it is less prone to detonation. properly tuned your engine will not have this issue.
2) Higher octane is advantageous only if the engine is fitted with a knock sensor that feeds the engine management system which in turn can automatically advance and retard timing as needed. Without this feature you are wasting money.
3) Premium fuel is required only in engines that have high compression and no means of automatically advancing and retarding timing based on engine load (again -- knock sensor needed).
4) If the manufacturer specifies premium, use premium. If they specify 87 - 89 octane, using anything other than that is a waste of money.