Eth vs. Non Eth seems to be more of an issue when sitting to a point.
Eth & gas are a mix, not a compound will separate from gasoline after ~3 months (or so I've read a couple places)
It is of note that with air-cooled beasts, both my VW's & my S200, there was noticeable difference on long runs in hot weather when the motors were pushing up towards their top temps.
The eth seemed to be a bit more prone to pinging under those circumstance, odd considering it has higher octane at normal temps, but there ya go. Either way the answer was the same. Back off the throttle and let it cool down a bit
Far as what's a better fuel, I have found some veracity to Shell's claim that their nitrogen compound smooths the motor out a bit, on my burgman, & even my RAV (my wife noted it without me telling her) but no difference in MPG or anything meaningful in terms of 101 running the vehicle. The SYM, & the S200 are pretty buzzy at a visceral level so tougher to say if there's any notable difference on them.