From what I can gather, have heard, read in various discussions and tested in 50,000k over the last 2 years...
Shell Optimax can dirty your plugs to the point of requiring changing them in 2 tanks
BP is refined to 98 octane, where most others are chemically enhanced.
Most sports bikes
will not run on 92 octane
98 octane will not offer greater fuel ecomomy, but will enhance performance (dependant on engine tuning and design etc).
Once you find a fuel your bike runs nicely on, pick a servo and always try and fill up there - I generally use the same pump

If you always use the same fuel and fill up after the same number of Ks, any change will be bike related and not fuel. This is easy for me as my return journey to work is almost exactly 100k, and my fuel light comes on at 290k. I fill up every 300k at the same BP servo and get very consistant results. When I'm commuting I use Premium (95 octane), when I go play in the twisties I fill up with Ultimate (98).
I tested a number of servos using a variety of octanes, covering 1200k with each pump, and I swear by BP.
HTH
Mike
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07 ZX10R since new, tracky TBA, KX450F, 87 CR250 restoration, GT MTB - I've got serious thrill issues, dude