How far could the legions travel in a day

[Robert Vermaat]

First, when you are marching long distances, you don't march in step. That is common HOLLYWOOD Garbage.
[..]
The shorter men are in the front of a long road march, while the taller men are at the rear, which enables the people with the shorter strides to set the pace.

Of course that's Hollywood. But I don't think anyone even suggested that.
It's nice to have short men in front and taller at the rear, but that won't have been any use for a Roman unit on the march.
Afawk, the Roman army marched in a formation where the contubernium had a fixed position in the column, enabling the column to form the designated front line as effectively as possible.

That means you can't mix up the men according to lenght and thus ease the marching. And, indeed, we don't know if the Romans knew that.

Oh, and, even when the short legs set the pace, that still means that the taller ones have to adjust their 'natural' stride.