Well, XP is stable enough for a development, I never had any problems with it (and I never get used to Linux on a client side). But I would never use XP on a server side for a production release.
(hide) If you want to play a game with an opponent of a similar level, you can define a required BKR range for a new game invitation. Then nobody with a BKR outside this range will be able to see/accept it. (Katechka) (show all tips)