I've been exclusively running 91 octane for the last 8 tanks.
The limited data I've got shows it gives me some MPG improvement (so takes the edge off the increased cost), and there are folks who say that the change in timing helps to reduce oil dilution risk (others here disagree.) Plus there are a few back roads here where I go in manual mode and wind the thing out.
I like the idea of using the sport mode button to toggle between modes...if you want to change shift points, use the manual shift.
My problem is I'm a low-risk guy, and would want to wait for the warranty to expire before doing this. Although I may change my mind. This would make a great Christmas gift to me!