If you don't have your own Castle link to change it, I would recommend staying with 6v. If I were to set it at 6.5v and you had heat issues, you wouldn't be able to put it back down to 6v.
All looks good on your setup, and it is certainly within specs of the BEC. It is a warrenty situation I would say, and Castle generally likes to handle the issues themselves. Since this was basically the first run though, I can call it a defective from the factory and handle it myself quicker than Castle. What was the order number? I can get a new one out with tomorrows mail.