pip, what's up man?!
I would go for a new stem over an old stem personally. those old cinellis are nice, but I don't know, new is new, and you are an animal, so I'd go for something that hasn't seen abuse yet.
just to throw yet another ingredient into the mix, I recently switched up to a salsa cro-mo stem and it is my new fav. have used nitto jaguar aluminum, SR, nitto pearl, and '80s cinelli stem and this salsa is stiffer and happier on my bike than any of the others...