I use Gasohol 91 for my Kawasaki ER6N and I read somewhere that I can get 10% more performance if I use Gasohol 95?

Filling the tank with petrol or gasohol with lower-, higher- octane ratings doesn’t damage the engine. In case you have used 91 octane and for some reasons need to use, or just simple want to try, 95 octane, the bike will still run properly.

This is not for all motorcycles, with older bikes, there may be some knocking due to misfiring, but the newer engines with anti-knock sensors are free from this problem. Depending on the age of the engine there may be some difference in acceleration and top speed when switching between 91 and 95 octane, or there may not be any difference at all for modern fuel-injection engines used by Kawasaki.

If there is no difference in acceleration, then there will not be any difference in fuel consumption either. But in the event that there is a difference in acceleration, it is possible that one of the sensors of your motorcycle are not working properly.