Took Chipp's advice and tried a Radiosity render with that "Indirect skylighting" checkbox on (in Atmosphere Editor's Lighting setup for Global Radiosity). 6Hr 17Min render.

I also combined slices from each of my Radiosity render examples for easier comparison.

My choice would be about 1/2 way between the top 2. That is, like the top one, but with more Radiosity gain.

My tutorial is updated for this new stuff.

_ jc...'Art Head Start' e-book
.......Art Head Start.com site Art skills for digital artists. Free lighting chapter, tutorials.