Hi Nick, In the past, I've successfully expressed a 130 kd eukaryotic protein in large quantities in plain BL21. I don't think size per se is a major problem for expression although I've heard others say they had problems with heterogeneous termination. I'd try the standard repertoire of techniques to improve expression. What has worked best for me in the past were 1) lowering the temperature of induction/expression and 2) using different tags.
It sounds like you've already tried many different parameters. Consider different expression hosts. ho