Brush Size

I have touched on this before but never did get a difinitive answer on it. It appears that TGE just does not like big huge brushes. On one project I am working on the helicopter lands on it and then crashes the engine. I am thinking this has something to do with the huge brush. It renders where earlier builds would just crash the engine when you tried to load it but I am still wondering if the one huge brush is the problem. I am also wondering how big can you make a single brush before you start to run into problems.