Just read my manual. On the CTS-V recommends 91 for better performance but can use 87. This darn thing has so much power, don't need anymore performance. My body can only take so many G's.
I am looking at trying to get better gas mileage thou. It would help if I could keep my foot off the pedal
That said, averaging ~20 mpg, goosing it a bit when I want my cheeks to flatten. Would the 91 give better mpg? From what I have read, it would avg out...more money in the tank but longer on the road?
What about getting a "mpg" tune/chip? No more power, but max mpg?