You might try doing a sectional render, not quite like Ghostofmacbethis suggesting tho. I've got something I'm working on that I wanted to change the lighting on. So I did a sectional render to see the difference. I was just doing simple renders for speed so I don't know if this will work for you or not. I rendered the whole thing with quick render and no antialias. Then I plop rendered half of it so I could look at the differences side by side. Could you do something similar? Render it with quick render so you have an image saved then plop render sections of it. Say plop rendering the top third with full render and antialias, then plop rendering the next part so they overlap slightly? I don't think I could tell where on render started and the other ended on mine, maybe it could help you.