Yep, when I do this kind of work I have to give up my filters.  So it really takes something fairly evenly lit.  I love using gradient ND filters and polarizers for landscapes so it can be hard working without them.  I think if I can ever take the time to learn HDR I can solve a lot of the problems with scenes where I would normal use a gradient filter.  One of these days I really need to learn photoshop.