Just bought the Q9 to my father and the Q8 to myself. There is a few differences, mostly minor. One important thing first: The Q8FN in the EU is NOT the same as the Q8FN in the US. So if you are from EU and read tests and read on forums about Q8FN. Make sure you know this difference. The US Q8FN has the name Q8DN in EU, and the one named Q8FN here is a bit different. Most important: Q8DN has full back-light Led and the Q8FN has edge-led, whitch is quite inferior some would say. Both still good high-end tv's. Strangely, here in norway the one connect box only came with the Q8FN and not the Q8DN.
Anyway. To fast say anything about the difference of Q8 and Q9.
Direct led back-light
Imaging prosessor: Q engine
Piqture quality index: pqi3100
Music effect / watt: 40
Conrrast level: Mega contrast
Direct full array elite
Q mastering engine
Music effect watt: 60
Contrast level: Q contrast elite
I dont think the differences are to big, mostly I think its samsung just using fancy names on almoust the same just to make their Q9 flagship unique. The full backlight is what makes both tv shine out from the other tv's below them.
The 500 difference in nits doessnt really do anything in a normal home i'd say. 1500 is still high compared to other tv's. (higher nits = better picture when there is much light, like in a tv-store. Nits is candela per m*2 or something, and candela is a mesurement for brightness)