Sakura is the one who is faster in body movements speed (not sure about who has a better reaction speed tho) but I don't think that she would beat Tsunade since she isn't fast that Tsunade can't react or properly react to which means that Taijutsu is the deciding factor here and not speed. Speed only becomes more important when it's fast that the opponent can't properly react to but as long as both of them can react to each other, they would still be able to perform Taijutsu techniques and the one with the better techniques and skill should win imo.Clearly this comes down to who has the superior speed; reaction, and striking be the most important.