I got a 48" C6 yesterday since it was on sale in my country. I can confirm it has a tandem oled panel, and it's noticeably brighter than my 55" C5. It's not quite as bright as the 55" G5, but it's way brighter than the 48" C5. (For reference the 48" C5 clips details at 900 nits, the 55" C5" at...
I compared the 55" G5, 55" C5, 48" C5, and 42" C5 over several months as PC monitors, switching between the displays each day to see which I liked best. I found that the dithering is just as noticeable on all sizes, but on the G5 it's much more noticeable at the same distance (I'd approximate it...