Gray (Fate) looks a lot like Saber and has similar abilities but those won’t be enough to win here. It is rare that the fake can beat the original after all. Saber still has better speed and power at her disposal which will really make things difficult for Gray. It would be extremely hard for her to keep up with Saber after all and a single strike could be decisive in this match. Gray won’t be able to counter in time. Saber wins.
Fafner Leorange is a strong Guardian but he did spend most of the series getting kicked around. Gray may not be the strongest Fate character around but she can still hold her own when the going gets tough. Her speed and power are both superior to Fafner’s. He may have a little more durability but it’s really not enough to save him when he will be the one eating the most attacks. Gray (Fate) wins.