I use tribal warrior outfit, more for the style than for my build, it's very light for 27 armor, i guess i have no malus except i die in 1 or 2 hit.
When i use cuir bouilli or sarranid guard armor, i feel slow, i prefer to be lighter (for wpf too), but it remains suitable, and you still have speed for footwork.
For more info about weight, athletic and speed look here :
http://forum.c-rpg.net/index.php/topic,3278.0.html Waltf4 made a very well detailled test.
I can't tell you for shield, i didn't had the occasion to test between 4 and 5 shield, but there is necessarily a little more. First gen i had 6 shield but it was prepatch so forcefield was bigger. I choose to have 4 in shield because my char is not centered on the shield, still it protects me from arrows and i can fight multiple enemies but i don't like to keep my finger on RMB, footwork is better (atleast for the fun).
Edit for Vibe : exactly i have 1h 142wpf, xbow 81wpf, but you can do 140, 80 and 22.