I just sold off one of 7 in the garage that was sitting idle. The Yamaha XT250 was good for 80 MPG on regular gas. That leaves the TW200 as the last carbuerated dual sport with 80 MPG in the garage. The rest are street bikes that run on 91 octane minimum. 2 Harleys, 2 Kawasakis, 1 Yamaha Roadliner, 1 Piaggio BV500. All get 42 to 55 MPG.
The following does not apply to ethanol blends (I don't know the math).
But octane increases in a nonlinear fashion, so that persons wanting to average, say, 90 octane, ought not to buy 90-octane "Plus" premium gas, but should split their tanks or alternate top-ups with 87 octane and 93 octane.
A fuel tank that is 50/50 blended 87 octane and 93 octane will actually have an octane number higher than 90, because of the nonlinear rate at which octane increases with added MTBE, toluene, TBA, or whatever octane-enhancer is in use.
So in a 20-gallon tank, a split 60/40 split between regular and 92- or 93-octane premium would be about right, and more economical than filling up with 90-octane "Plus".
This is some admittedly dated wisdom gleaned from a "downstream" article about gasoline-blending that appeared in Oil and Gas Journal about 1982, when the EPA was just starting to make refining a hairy proposition with numerous bans and demands for low-volatiles summer blends, and by the way driving hundreds of small, 10,000-bpd refineries out of business (deliberately, of course -- so they could regulate the survivors more easily and more closely).