His IAM only dropped to 0.96 , yes he could continue to run 91 no problem.
Tip in knock that causes the IAM to drop in the 2000-3000 rpm area has a lot to do with driving style and how aggressive you are on the throttle at low rpm in a high gear. I can get it to happen on E85 thats 105+ octane if I drive aggressively in that area in high gear.
By the way your pulling about -1.5 degrees FLKC arround 5500 rpm so 91 not all that good
http://datazap.me/u/stugray/za1ja00c...-35-41&solo=35