I'm no expert, but i'm not a fool in relative terms. Meaning I read stuff and try to weed out the hype from the truth as best I can.
I currently have a rule of thumb when it comes to fuel choice when running not just my Rocket, but all my petrol powered machinery/cars. I'm based in the UK, so fuel pricing does have some influence in my decision making, to some extent.
When i'm using the bike regularly I use E10 95RON petrol but if i'm not running the fuel tank down regularly, I use E5 97RON petrol, which should help reduce the chance of water contamination in the tank and extend the octane value of the fuel.
Whilst I understand that modern 'high performance' engines run better on higher octane fuels, I think that this logic only really applies to situations where you are trying to get the max BHP out of the engine, and 95% of the time on normal roads, you're not doing that.
Regarding ethanol content in fuels causing premature fuel line and associated component failure (eg, lines/hoses, pumps, filters, plastic tanks etc...) Most modern vehicles have been revised to combat these issues. Not completely but better these days than say 15 year old vehicles for example. At least the Rocket has a steel fuel tank and not a rotomoulded plastic one, so thats one big ticket item not to worry about.
I'm interested to hear what others have discovered on this subject.