[Musikmann]

Potentially there could be problem(s) with your engine. It is engineered to run on 91 octane and that is what I would use if I were you. As has already been implied on this thread, a 10 cents/gallon savings is meaningless when compared to what it might cost in engine repairs in the future.

One thought though: In my area, Plus is 89 octane and Super is 93. If that is true in your vicinity, you could save 5 cents/gallon by pumping half and half of those 2 grades.