I voted for 7, but I'm not really sure. I personally think 6 is a fine number. In fact, 7 may be too much for a party.
However, since this is an online game, there will be periods where one or more players can't respond for a shorter or longer period. If, say, 3 players can't post (this has happened before), we're down to 3 which is a bit few to run this game. 7 gives us a bit more "resilience", so Flea doesn't have to act for both the opposition and half the party. At the same time, it drags the game slightly down with too many players.
In the end, I'm really unsure myself, but I'm slightly in favor of 7.