When to start "trusting" your PT stats?

[soweak.]

Now I'm not talking about personal statistics, but those of the other players as they enter the game. I think it might be a hole in my game that I either overly rely on PT when a new person sits down, or i don't have enough hands on other players.

My autorate is set for 25 hands, is that about what everyone else uses?

Also if anyone could point me to a good limit autorate rules set I would be appreciative (and yes I have searched for one).