Not exactly your query, but...
1. Viton is a tradename by Du Pont for a perfluoroelastomer.
You want a ring gasket: your choice will be determined by the ring supplier, won't it? So I suggest to ask ring manufacturers. Their job is difficult enough that they experiment little with materials, so your whole choice is in their catalogues.
Or are you planning to produce the rings? Then, get your inspiration from their catalogues.
99. If you read German, I emphatically recommend you a handbook (89€): Kunststoff-Tabellen, by Bodo Carlowitz
. Very detailed usage and production properties, all polymer and elastomer variants, trade names. Used or older ones are uncommon, alas.
If you read French, get some access to the Techniques de l'ingénieur
, one of the volumes about Plastiques. Complete lists of trade names, direct and reverse; some synthetic properties. At some 3000€ a volume, you can find them at the French and the European patent offices in France, and at La Villette's library.
Well, it's just like for mechanical engineering, fluid mechanics and a few more: to have good books, learn German