Mark, Kix -

Many thanks for the detailed responses. As you might have guessed, I'm trying to get the render time down for my short animations. For 1280x720 frames, I'm getting ~8 minutes with full Indirect on a wide angle interior, and less than 30 sec with AO, a big difference in the two day 48 Hour contests. I hadn't thought about "light grids", but I have these Tim Payne light domes for Carrara but have not yet tried combinations with AO:

http://www.daz3d.com/carrara-skies-lightdomes-1

As I recall, they also have strengths around 1% for the three presets: 41, 141 or 641 lights. Not sure about the render times, lots of shadows to calculate?

So more experiments coming up.