WOW lot's of info here (whether correct or incorrect) lol.
There are two different things to consider: octane rating and ethanol content.
Octane rating: Use what is listed in the manual at a minimum. Higher octane than needed is a waste and does not increase power or any thing like that, but it is safe. Do not use octane that is lower than required or you will get detonation. Also, running much higher octane than required can cause carbon deposit build up. Octane rating is defined literally as the resistance to detonation, a higher octane rated fuel burns slower and has more resistance to detonation than a lower rated octane fuel. Typically, higher octane is required with more compression and more timing advance. Run what's required by the manual. The xb's I believe require 91 octane. Here in FL usually you have 87, 89, and 93, so run 93 in this case. If you have the choice between 91 and 93, choose 91. If you really want to get it to 91, then fill half tank of 89 and half tank of 93 and "wala" you have 91.
Ethanol content: Again, like the manual says, the 10% ethanol mix will not harm the engine. Now, if I had the choice to buy pure gas I would, because it is better. It will get slightly more mpg and power (ethanol contains less energy than pure gas per the same volume). Ethanol also will deteriorate rubber hoses, gaskets, o-rings, etc. in time. Using a 10% mix isn't a huge deal, but I would never run E85 (85% ethanol) in my vehicles(and my truck is actually a flexfuel vehicle).
Here in Florida I think that practically all gas is 10% ethanol blend. I don't remember the last time I saw a pump here that wasn't(except right next to the drag strip...).
If the pump says "91" then it is 91 octane, whether it has 10% ethanol or not.