Depends on how the bike is running on what you have been using.
I would say 89 at the least. I get a little drop in milage with 87 which is around 85 octane equivalent with ethanol mix.
They don't use the same formula to get octane rating with ethanol blends.
So if your using the blend your guess is good as mine.
I avoid the "Blends" when ever possible. Only a few places left to get the good stuff any more.