Good question! Thanks for re-starting this conversation, too.
So, from my limited experience (I've only run my Prussian BC in one game), it seems like DW BCs will do just about what they did in real life; tear up ships of their size and smaller, but generally get smashed by anything larger. As was pointed out in the PE tactics thread, there is also quite a range between the different BCs for the different nations, as far as weapons, generators, and the like. This means that they are going to work quite a bit differently from fleet to fleet, it seems.