Also, would be nice to see what effect shields and sheathed weapons have on speed (both run speed and swing speed).
My testing suggests that the engine uses a single, total weight for the running speed calculations. This weight includes all items your character has on them: worn, sheathed, or unsheathed. Holding a weapon further reduces running speed based on the weapon length and weight. Holding a shield does not change running speed relative to wearing that shield, unless your character is holding one shield while wearing another shield; in which case, there is an enormous reduction in running speed.
Only armor weight appears to matter for attack speeds. Holding a shield does not change the time taken to complete an attack. However, the delay between blocking an attack and beginning your own attack may be different if you block with a weapon compared to a shield. I would assume that the difference depends on the weights and speeds of both the attacking and blocking weapons and the shield.