I would actually suggest that the option SHOULD be placed on the 19x19 board. Remember, the 13x13 board is ONLY here to accommodate the WebTV users.
As far as ratings go, I agree with Dmitri that it is a problem to use restricted and unrestricted games together in calculating a single ranking. I disagree with his suggestion of only allowing unrated games for the unrestricted variant. That’s not right. Creating a separate game on the site would work. How about calling it Original Pente, since that’s how the rules originally were. :-)
(verstecken) Wenn du Spiele mit ähnlich starken Gegnern spielen willst, kannst du beim Erstellen eines neuen Spiels die BKR eingrenzen. So kann niemand ausserhalb des gewählten Ratings das Spiel annehmen und sehen. (Katechka) (zeige alle Tips)