The castle bec has a maximum input voltage of 26v, so if your going to use more than 6s I'd look for a different one.
The UBEC Mikes sells can take 40v, so I don't know if 10s right off the charger will be too much.
http://www.rc-monster.com/proddetail...=6vubec&cat=21 Out of stock of course.
I think dimension engineering makes some even higher voltage ones, but I've never looked into them.