Encumbrance.
It is possible that by stamina affecting encumbrance, encumbrance will indirectly change speed.
But in Oblivion, encumbrance didn't change speed. :sadvaultboy:
There doesn't seem to be a way to easily introduce fatigue and/or encumbrance based movement penalties by just tweaking game settings values. This means that it is not possible to have NPC and creatures "slow down when puffed or burdened" without adding scripting to every single NPC/creature. This makes Burden-based poisons pretty much useless unless they are strong enough to overburden and pin them down. Anything less than 100% encumbrance doesn't slow them down at all, but the final straw that overburdens them suddenly pins them to the spot. Draining Fatigue does help reduce the damage they deal, but it doesn't slow them down when they are chasing you.
This doesn't seem to be ideal. I hope they refine the formula to add encumbrance to the equation. Burden should work too as expected.
edit: Yes, Morrowind works as expected. "Encumbrance also has an effect on your Speed. In this case, it is the ratio of your Encumbrance to your maximum Encumbrance that determines how much you are slowed by what you are carrying."
I wished they would add multipliers based on races for three main attributes, H/M/S. Even 1.1, 1.2 kind of deal will provide lots of
potential difference between races.