As far as I can tell.. the last 2 renders I've posted in my gallery are about the same image quality.  The scenes weren't very big either.. just model, clothes, hair, backdrop.  First was rendered w/o the cube and 2nd was.  I let them bake overnight while I'm sleeping and I can just about set my clock to my length of sleep(solid 6 hours).  The one w/o the cube took nearly 1k passes to gain the quality it did; whereas the 2nd one took barely 400.  I'll check again with my next 2 renders to see if it wasn't a fluke.

 

And I've noticed with RC3 that my samples/sec is staying about the same; but, I'm getting a massive increase in efficiency.