I use 91 Premium fuel in all of my seven bikes incl my 2007 KLR 650. Reason is that regular rots faster, but in the winter I also use Seafood as an additive. Some of my bikes respond to premium, but no real mileage gain. In No. Nevada we get crappy ethanol in our fuel from Oct 1 to Jan 31 in the two most populated counties. Other areas in the country may have no ethanol or year-round ethanol mixed in for air quality rules.
I can report that Race Gas from Summit Racing does make a different in bike engines, but at $1.00 per fluid oz to raise the octane several points is used only for "special occasions". This area lost it's VR Fuel Station that carried 100 octane for Hot August Night performance cars, but at $8.00+ per gal it was again a "special occasion" fuel of choice. Maybe I need more special occasions??? Wish our 23 ft of snow in the Sierras during January melts off this spring for riding.