In the lighter hitting areas I have found that 18g mild steel works for everything but thighs and forearms (and helmets of coarse) -so 18g SS should work great. I have a 4' piece of 18g SS out in the shed that has mine name written all over it -if I ever get the time to remake my armor...
(^_^)
------------------ Hjalmar of Sognefjord House Bearkiller Barony of Grey Niche, Meridies.
"True nobility is not measured by being superior to another, but rather by becoming superior to oneself."
Anything else is just added weight, for the most part. This should be plenty to keep you safe.
If someone hits you hard enough to cause bodily harm while you are wearing 18ga in the above mentioned places, they are hitting too hard for SCA combat, IMHO.
Well technically speaking 18ga mild is legal for everything except the helmet since the definition of hard over soft is for 18ga mild steel or equivalent with no requirements to have an equal weight.
------------------ The budding mid 14th century German Transitional guy. Mad Matt's Armory