Yamaha recommends 87 octane for that bike. The only reason you would need to go above that is if you are experiencing knocking. The occasional "backfire" you're hearing is because you're dumping extra fuel onto the fire without providing the airflow required to properly burn it, since you're sitting at a stop light when you crack the throttle.
Placebo effect is powerful on the mind, but running a higher octane rating will not improve your bike's performance if you're not experiencing knocking. The claims of additives to clean your fuel system are hype too. That stuff doesn't exist in the fuels at a concentration required to have an impact. Run some SeaFoam if that's what you're looking for.
It also should have no impact on your average mpg. I see better mpg on the rare occasion that I stumble onto fuel without ethanol, but that's harder to find in my area nowadays. I recommend you just run 87 octane in that bike...and so does Yamaha.
Ben C - Cary, NC
2001 XV1600A Road Star
2003 XVS650A V Star Classic