Now that you jogged my memory, I figure your right about where the noise was coming from. Awhile ago I did some front lit tests with quality set at 32, 64, 128, 256 samples at 320x240, to check rendering time vs. quality. At least for 320x240, 64 seemed to be the bare bones acceptable lower limit. For that scene at least.
I will test your atmosphere doubling idea out today. Which brings up a point about TG2. I find that TG2's atmosphere is simply stunning, but that "volume of light" quality it has (which matches photography very closely) does not carry over into foreground areas all that well. For foreground elements I get the sense that everything is in sort of a "light vacuum" environment like conventional ray-tracers, and increasing GI quality only partially addresses the problem (I must admit, I have not pushed the GI quality to its limit yet, at the expense of a huge rendering time). For instance, in all the images in this thread, if you crop out the terrain, the sky approaches photorealism, yet if you crop out the sky, the terrain in the foreground looks like an illustration. Light just isn't bouncing around all that much in the foreground and getting into the nooks and crannies enough. I suppose I could put a light source behind the camera, or a huge reflector, but my impression is that the problem would still remain.
