All is pretty well explained here:
http://forum.c-rpg.net/index.php/topic,29377.0.htmlBasically, body armor reduces damage taken and hitpoints its the damage it can take in total.
Pretty much like armor and HP in players, same concept
Thats why steel shields are good against non-shieldbreakers (absorb most of the damage) but against shieldbreakers, they break very fast (it pretty much ignores the armor).
Speed is how fast it starts actually blocking. Thats why some fast shields might block before they are fully up, and the slower ones sometimes dont block even though they are fully up.