What fuel grade to use.

Remember that the difference in higher octane is basically that higher octane gasoline burns slower. I may get a lot of flames for this, but this is what it comes down to. Now many will say that the "premium" gas is inherently better in other mysterious and undefinable ways, but I have no indication that this is true. I've used regular gas in all my cars, boats, motorcycles, boat, chainsaw, weed whackers, generator, and lawn tractor for what amounts to like a vehicle-century and have no fuel-system related problems I can recall. In fact, a completely repeatable experiment I ran on my '75 GL1000 (a carb-equipped bike) was that use of premium gas caused gas mileage to decrease. Every. Single. Time.

The only high-octane fuel I use is 100LL in my airplane because that is all that is allowed because of: 1) Certification Limitations and 2) That's the only gasoline you can find at most airports. I actually could use a lower octane, lead-free, ethanol-free fuel if 1) Appropriate certification paperwork were provided by the manufacturer and 2) Where it actually becomes available at airports. FYI, 100 LL, simply with tetraethyl lead not added would fit this bill.
 
I live at 4400' ASL, and our "regular" grade is 87-octane. It works fine. So does 89-octane when I'm at lower altitudes. Like Rich said, higher octane does not increase power in any way. All it does is allow higher compression ratios (which can create higher power). It has fewer BTUs / cc/gal/liter/.
 
I confirm the other posts...I've tried different grades and have seen no noticeable change in performance...so I use 87 regularly now.
 
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