o.k., thx fr renders, bill. they look very good IMVHO.  the new sponza atrium comes with
a gi_flag matl. for which they forgot to distrib. a tga file, and I found that it's badly UV-mapped,
e.g. for a rect. img. to fit it in poser, the central hanging curtain needs Uscale ~ .29, Vscale~ .58.
in render 2, luxrender:

• how many bounces?
• what was lite source?