At what point do you six star Bernard?

There is a lot of discussion about whether or not to six star Shannon, but almost everyone agrees that Bernard works fine as a five star in Giants. However, most Bernards I encounter in the Arena are already level 40. My Bernard works great in Giants as a 5 star, and I recently used him on several floors in my first ToA clear. So even though he does his job fine the way he is now, I still use him everywhere. Therefore, it might be better to six star him - but on the other hand, I have lots of other candidates that would benefit from it more. I guess you can see my problem... :)

What do you think?