Its very dependent on the vehicle. Vehicles with specially tuned, high compression engines (motorcycles, sportscars) will do better on high octane. Most others will get better mileage on low octane. The only other factor to consider is that in some areas the premium fuel is ethanol free, and the regular octane is an ethanol blend.
This would suggest that even though your bike has proven to run on lower Octane, as you pointed out, you will indeed see better performance with higher octane because your engine design (compression) is high enough to take advantage of a higher octane.
One thing to consider is the performance increase vs the cost increase. If the fuel economy increase is 5% but the cost of higher octane is 8% then maybe it's not as economical (of course better fuel economy is kinder to the planet and higher octane might perform better).