Straight up speed is not Barzal's game, I don't know how he'd fare against the noted speedsters like McDavid and Larkin. I think they are at another level when it comes to pure twitch speed, Grabner as well.
Barzal's technique is almost flawless, he looks like he'd kill it as a speed skater in either short or long track. He's ALWAYS moving his feet, he's always crossing over. I remember seeing this in his draft year:
John Williams - Central Scouting: "He's the best skater I've seen in the WHL in terms of his east-west game while creating time and space with his feet. He has great vision and puck skills."
You'd be hard pressed to find a more elusive skater than Barzal right now. With premium vision and instincts, he uses his skating to full advantage. It looks comical how he can play keep away from everyone and he's not doing it with unbridled speed.