I've been considering that same thing, Ring!

Here is what I found:

Run - is affected by plate, and can not be sustained. For the longer travel, we'd fall into the category of 'Hustle'.

Hustle - A hustle is a jog at about 6 miles per hour for an unencumbered human. A character can hustle for 1 hour without a problem.

Hustling for a second hour in between sleep cycles deals 1 point of nonlethal damage, and gets worse if you keep going. A character who takes any nonlethal damage from hustling becomes fatigued. A fatigued charactertakes a penalty of –2 to Strength and Dexterity.

Eliminating the nonlethal damage also eliminates the fatigue. (So, cure minor wounds would cure the fatigue)

(Hustle is affected by if a character is encumbered, but plate doesn't inherently cause an issue.)

http://www.dandwiki.com/wiki/SRD:Movement

At this point I would translate that as either 6 zones or however far a character can run in 1 hour.
A starting point at least!