On a stock compression motor, you should be fine with 91-93 Octane, whichever they sell in your area. Try to buy gas WITHOUT ethanol if you can. I know there are a lot of people out there running the cheap 87 Octane. Nowadays with the poor quality gas and ethanol blends, you are taking a chance with that.
We store our machines with 100LL Aviation fuel, and I would run it all the time if it wasn't $5.25 a gallon. Plus, you don't pass many airports out on the trails! That is some good gas though. I highly recommend it for at least storing your sled over the summer.