75msuar

I don't know about the advancements of gasoline, but the different between the 91 octane rating in the owner's manual and the forum's recommendation of 87 is the different ways of measuring octane rating. The owner's manual shows 91 octane using RON method, which is the equivalent of about 87 octane using (R+M)/2 method. Most pumps today in the US use the latter; look for somewhere on the pump and it'll show (R+M)/2. This wiki is particularly helpful: https://en.wikipedia.org/wiki/Octane_rating#Research_Octane_Number_(RON)