V8 gaskets

Just a question for those in the know. Why is there an option of a fibre gasket for the valley on the 3.5? are the tin ones prone to leaking?
Also has anyone used the Payen gasket seat and know if it comes with valve stem seals?
I am currently looking at putting an order in to get these parts out of the UK so i want to get it all in one go first time.
Thanks for any help

The fibre or composite gaskets make a better seal that tin ones and don't rust, they also do composite cylinder head gaskets too. Any good cylinder head gasket set should come with valve stem oil seals too.