The difference as I see it with both Ehlers and McDavid is that its functional speed vs just speed and they use their speed much more often than other players.
I will use the goofy example but I think it fits. My 8 year old son plays on a pretty good spring team and they all move around the ice well. The moment the coach blows the whistler and they start doing full laps at top speed they all look so much faster because its straight line speed and they don't have to worry about handling the puck or playing hockey.
Ehlers and McDavid can function at a high level with the puck on their stick, head up, and making plays. The only other guy who consistently uses it in a similar fashion is the pre 2016-17 Matt Duchene. Wheeler is fast and uses speed as a weapon but it's not the same as Ehlers because Nik has a better burst, is much more creative, has better edges, and can change direction on a dime. Blake gains separation by getting to top speed and blowing past and around players and maintaining that speed. Nik can do that but he can also gain the blue line going north south then cut straight sideways and go east west without losing speed and drop everyone.
And then he'll miss the net.
Maybe the Baltic Bros can help each other. Skating tips from Ehlers, shooting tips from Laine.