Selfbow,
As a BW owner for a bunch of years, and as someone who has owned the "basic" Graybark, and the more "exotic" X-models, I can say that IMHO, there is very minimal performance difference between bows of the same model (For instance, comparing a PMA-Graybark to a PMA-X)
Where you might notice a slight difference in performance or "feel" is when you compare a longer-riser PMA to a shorter-riser PSA, for instance; or a 60" PMA to a 64" PMA, etc.
IMHO, the X-model just gives you a prettier bow, but it won't perform any better than the tried and true "basic" Graybark or Autumn Oak.