So, I tried two different things.
1. I first used the 5.0, 5.7 and 7.4 bins and an Excel sheet to find out where the approximate AE values for a 6.6 machine should be. The bin #34 attached was the result.

As can be seen in the log "notenough", she still backfires.

2. I then copied all the AE values from the 7.4 bin to bin #35. Not only is the backfire issue still there (see log "stillbad"), I stopped logging right after the backfire to make the backfire easier to find in the log. But throttle response felt even worse than before, so I also did a fully warmed up log ("warmedup" keep in mind it was 14F and snowing during the logging run, so any hectic throttle activity is backing out of slides).

As always, any input is appreciated - I truly am at a loss.