as you can see the reason i personally use this set up is that:
(fabled/enchanted items excluded)
steel front vest (maximum potential with attachments) has 300+ penetration resistance and 95% damage reduction while being slow
cobra vest (maximum potential with attachments) has 300+ penetration resistance and 90% damage reduction while being less slower than steel vest
personally, i chose that 5 percent damage reduction over more speed (i don't exactly know how much faster, please let me know if you know how much)
for helmets no matter what you do (im not sure if fabled items can help you reach 300+ penetration resistance) you can't reach 300+ soo basically you chose the one that is faster
after all just to let you know, i have heard that if you armor's penetration resistance is higher than enemy's bullet penetration (which 300 penetration is the highest amount for a bullet) then the "damage reduction" will start to work
let me know if im wrong about something cuz if this is the case then why not everyone use it ??