Did some more experimenting with various settings and found the following:
High Panel Brightness introduces SIGNIFICANT amounts of noise to the image, especially near black. I verified this by comparing near black test windows on the various panel brightness settings. There is very little difference between low and mid in this regard, but high is awful: the entire picture crawls.
On mid panel brightness, the amount of green push (green brightness relative to the other primaries) varies with the contrast settings. On my set (which will not be the same as yours) any contrast above 76 seems to achieve its additional brightness primarily by boosting green. On a set with a calibrated grayscale, the result is green flesh tones. Contrast must be backed off to compensate.
Also, keep in mind, on mid panel brightness, there is a governor on the contrast setting so that increases above 80 don't do anything at all. I imagine this is because going above 80 would seriously compromise the PQ.
You can raise the contast above 80, but luminance does not increase. It's smoke and mirrors.
I continue to be dissapointed by how dim this television is. Ideally, in a room with ambient light during the day, I'd like at least 35 ftL -- on my set, this simply is not achievable on mid panel brightness. Calibrated ft.L (including grayscale and green luminance adjustments) on each panel brightness mode are as follows:
1) Low = 19 ft. L (unwatchable during the day, especially on dim content)
2) Mid = 30 ft. L (approaching acceptable. I'd like another 5 ftL, but no dice).
3) High 40 ft. L (the compromises of high panel brightness are not worth the increase in luminance).
As noted previously in this thread, there appears to be extreme variation in the brightness of these sets. Some have been tested at much higher brightness levels than mine, and I suspect others still are dimmer, but I have no idea where my set lies on the Bell curve.