Now this is tough. They are pretty much even in physical power, and Saber can probably deal with the abilities of Excalibur's Ruler and Transparency with her magic resistance and instincts, although Xenovia hasn't mastered that first one. Saber has a bit of a durability advantage, but not so much she can't be hurt if Xenovia lands a clear hit. I'd say Saber has a slight edge with her instincts. Not sure about Xenovia's reaction time, depending on how high it is it might tip the scales in Xenovia's favor.