Changing from unleaded to premium gasoline

[dr. d]

If you can achieve a higher mileage while using a higher octane gas vs a lower octane, is it still psychological?

some questions to ponder when comparing fuel performance:
is the difference credibly measurable?
are we talking of numbers too small or too erratic, as to be roundable to zero?
may the improvement not be due to a change in driving habits / traffic / road conditions?
are we talking about a perfectly good engine, or are we talking about a modified engine, or a tired engine with lots of cylinder deposits, etc?
is the engine intelligent enough as to modify its adjustments in order to maximize the higher octane?
was the driver originally using a lower octane fuel than that recommended by the manufacturer, then changed to the recommended octane, noting afterward the improved performance..?
DID the manufacturer intentionally understate the engine's octane requirement, in an effort to introduce lower fuel costs to the potential buyer? (heh heh.)

if threader started by saying he actually experienced improved mileage and not just read about it, then it becomes a more meaningful statement that would offer a potentially livelier argument in search for an explanation..