You cannot run lower octane than the tune. It has to do with fuel stability properties of the higher grades.
If you dont really want a 91 performance just stick with an 87 performance tune because there will not be a worthwhile difference between an 87 and 89 performance tune...you could also bump the timing up on an 87 performance tune if you are running 89 in the tank.
Yes, you can run the canned tune until the custom tunes come in.
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