I wish I could see/feel the difference in 89/93 over 87 octane. Then I would be tempted to pay 20+ cents/gallon more for it. But I've never noticed any difference in either performance or mpgs in the several times I've tried multiple tanks of the higher octane fuel.
The only difference I've ever noted was using nonEgas for a 7 month trial. I carefully fueled (overfueled to just below the brim so as to be consistent*) and documented a respectable gain in mpgs.
* Note: that was before I became educated about the issues associated with overfilling the tank.