Movement on the Shadow Plane

[OldManAlexi]

It is stated that the Shadow Plane can be used to cover great distances quickly. Are there any rules on how much faster you can move there compared to the Material Plane?

Shadow Walk gives a flat rate of 50 miles per hour. Would that mean that any creature, no matter how fast it moves, would progress at a rate of 50 miles per hour or should we assume that 50 miles per hour corresponds to creatures with a speed of 30 (aka normal human speed)?

[Alitan]

I'm pretty sure that the speed of the creatures involved has little to no bearing upon the (relative) rate of movement via the plane of Shadow: you're pretty much folding space as it stands by ducking into Shadow; the 50mph figure represents that fact.

In fact, it would make more sense (given the kinda perverse nature of the plane in question) that moving faster or slower doesn't make a difference.

Time keeps on slippin', slippin', slippin'... into the future.