Magic projectile speed doesn't take race weight into account
Morrowind scales the speed of projectiles (at least magic, I don't know about arrows/bolts/throwing weapons) with the player's race weight. So projectiles fired by male Orcs travel at a much higher speed than those of female Bretons, for example.
With an encumbrance of 0 and a speed of 336, a player should be able to travel at nearly the same speed as their magic projectiles in non-diagonal forward movement, regardless of their race.