If the hesitation you are speaking about occurred on the run that you showed in your datalog, it was caused by the UTEC pulling timing in the 5600-6000rpm range. Dropping from 23 degrees to 15 degrees and back to 23 degrees in a matter of 200-300 rpm will cause a noticeable hesitation (by design!).
Since your FJO says you are running rich, I would take out 1 degree of timing from 5500 to 6000 rpm and see if the knock goes away. If it does, you may be able to lean the car back out to 10.5-10.7:1 on pump gas (as long as knock does not return). If it does not (and you are sure you are rich) take out another 0.5 degree and keep going.
A BOV opening and closing under boost will also cause a surging, but this is an unlikely event. It should be easy enough to replace the BOV with the stocker, however and rule this out. In any case, you need to get your WRX running knock free first through some tuning.