I remember something mentioning she had a better average speed than even Lancer, and that Cu only outranked her on burst and 0 to 100 alone. Anyways, if the idea is moving so you don't get hit, the less weight, the better. Plus, she could very well try to bind Saber as a distraction technique, especially if she hid it with another attack to trigger Saber's instinct and divert her attention, though I don't know how reasonable that is. I think it's a very fair matchup depending on the efectiveness of Medusa's ninja skills.