All shields that have 8 weight or higher are 2 slots, so I doubt they'd make an exception for the round huscarl's shield. 4 shield is all you need, use an elite cav shield if you want rounded shield, or a knightly heater if you want a kite shield.
100 speed + high "body" armor = boss shields.
I would love to use the knightly heater shield, but being a nordic style faction I'm S.O.L. (jelly of 33 armor).
I'm not positive (about to start a thread asking the question) but I'm pretty sure your melee weapon speed is throttled down to whatever your shield speed is. So at 80 speed most of your 1h weapons would swing super slow. That's what I've been told anyways, I don't think it's a 1:1 ratio though.