I've been doing pretty much what Sam is doing, with a bit of tweaking. Rendering in Draft with the right settings and over black, does give equivalent renders to production, and in a much faster time. I'm glad I continued to pursue a solution to this because it's made my poser life sooooo much more pleasant :)

"It is good to see ourselves as others see us. Try as we may, we are never
able to know ourselves fully as we are, especially the evil side of us.
This we can do only if we are not angry with our critics but will take in good
heart whatever they might have to say." - Ghandi