I brought my Tbird in for the initial 500 mile service. I was having problems starting it until I did the 12 minute drill to reset the ECU. Now it starts ok but I did ask the dealer about doing a Tors download (eventhough I have the stock pipes). They recommended not to do it. They asked if I was putting regular octane gas in the bike and I said that I was actually putting in premium. They said that with the most recent ECU downloads that I should use regular octane. I said what about the middle octane and they said no, don't even use that, use regular. Anybody doing that?
The manual warns strongly against "lugging" the engine or causing it to knock. The standard recommendatin is 87 octane if memory serves, with the advice to use higher octane if knocking is occurring.
When I bought my bike the dealer told me to use premium because "Why risk it?" I started out with the 91 octane premium, then switched to 89 mid-grade and have used that without an issue ever since. No knocking. I have considered trying 87 octane but haven't yet.