A speed boost to the smaller shields seem a little redundant. From what I can tell of my experience fighting shielders, it's already a "I hit-you hit" dynamic with those shields. I don't see any reason for increasing the speed of the shielders, any faster and they'll be almost capable of out-spamming me (and with my build, they really shouldn't).
Well the speed on the shields wouldn't increase their actual attack speed, just the responsive speed of the shield. IE: A 1her without the shield is X speed. When using the shield it suffers from a speed malus due to raising and lowering the shield (affecting counterattack speed, feinting, etc). Increasing the shield speed would simply lean this more in the direction of the unshielded 1her responsiveness.
Currently there is no reason to use anything but the huscarl except for personal taste and style. In every area, the huscarl is the hands down best shield overall (Coverage, speed, durability.)