I believe that the weight of all your items affects your speed in the same way.
BUT also you get additionally slowed down depending on what you have in your hands (your animation of running).
1) Empty hands, 1h, 1h + shield, 2h/1h (like morningstar, longsword etc), bows, throwing - no penalty.
2) 2H - some penalties.
3) Polearm, xbows - even more penalties. Or maybe less. I don't know.
You can see the difference in animations when you run with these types of weapons, so I think it really depends on animation (some people say it also depends on the weight and length of your weapon, not sure about this).
So:
- You would run faster using Heavy Bastard Sword (weight 2) than Two Handed Sword (weight 2) because of different animation.
- Sheathing your shield doesn't make you run faster (doesn't change the animation of your hands while running)
- Sheathing your 2h, polearm, xbow and such - does make you faster.
- The difference between throwing axes and jarids might be if you use it in melee mode (1h for axes and polearm for jarids). If not, then it must be because of the length of jarids, I guess.
PS: note that any sheathing/unsheathing slows you down for a second, you should't consider it as actual slowing in the long run.