If we're going by pure speed and at least some semblance of puck on stick as well (not just off the puck), I can't really think of a high-end prospect faster than Mcleod, Kapanen right now. They have a similar gear to young Duchene but not quite at McDavid level...where he can just glide around at top speed.
Kyrou, Pujlu, Gauthier are others that are very fast as well but they don't have the in-game top speed of the aforementioned, IMO.
If your talking about all around skating, edges, pivoting, the list would be a lot longer.