Alright, here is my take on the X-Sabers:
1) Since obtaining my 3rd Fulhelmknight, I have done some extensive testing on the standard, full X-Saber build and I can safely say it is HORRIBLE.
2) From what I can tell so far, the Unexpected Dai and Galaxy Serpent/Piranha deck is a bit less crappy, but also HORRIBLE.
Conclusion: Until we have more good 7-star generic Synchro monsters without having to use skills that completely mess up your deck's consistency, X-Sabers will remain dormant in serious PvP.
Good luck to myself building Six Sams Synchro deck since that's one of the rare boxes I nearly completely skipped due to lack of gems and funds (0 Grandmasters = no Six Sams Synchro for me).