I did some more datalogging, and the amount of timing it is pulling here (same test scenario) would be easily taken care of with 93 octane fuel. I'm starting to think it might be ghost knock as the vehicle speed increases. Something must be fluttering/vibrating at a similar frequency because the KR trend isn't increasing.
I punched the throttle to pass and it only pulled a few degrees, and this is at a slower vehicle speed. Total spark advance, even w/o knock retard, is fairly low at these airload and RPM cells. Looking at the stock BKT/MBT tables for the Focus RS/Mustang/F-150, it's not surprising.
Once I finish this tank of 87, I'll switch to 93 and do more testing.