Oops! But, this whole site is about running tunes, this is for enthusiasts!
That said, the bottom-line is this: Run 93 or you don't get the same power that the car is rated for, 87 is minimum for safety, but to me that's dumb to even risk the low-end, run mid-grade at least if you can... If you only have 91 octane available, you lose a bit of power compared to 93 but you also can try adding 1 gallon of e85 to the rest 91 fill-up. This will raise your octane and should keep you no more than e15 which the stock tune can handle, but the safest way to make power is to get an e30 tune if you have e85 available, then you are doing like 3 gallons of e85 to the rest 91, but you need check your actual ethanol percentage too, some e85 is actually as low as e54, but there are online resources that will tell you what you actually get in your area for what time of the year... I'll leave it at that, sorry if I over complicated it!