Running all 91octane tunes isn't a problem in the least! As long as you have access to 91octane or higher, you'll be set. It's also not a bad idea to ask for an 87octane tune in case you run into a station that has poor quality fuel or only 87octane.
The beauty of owning an SCT SF3 is the tuner can hold up to 10 total tunes. Plus, you're enrolled into our Free Tunes for Life program and have access to as many tune combinations as you wish. So, I'd suggest picking up your three favorite 91 octane tunes, then submitting another Bama tunes request
here to ask for another 87octane street tune. Once all the tunes arrive, they can all be stored on your SF3 hand held.
If you have more tuning question, feel free to call up one of our Bama Tuning Specialists at the number in my signature. They'll be more than happy to answer any of your questions!