Here are the differences I see:
- Dynamic contrast ratio of 30,000,000 to 1 on 8000 and 7,000,000 to 1 on 6500.
- Clear Motion Rate of 960 on 8000 and only 480 on 6500.
- Micro Dimming on 8000.
- The 8000 has ability to upgrade hardware over the next 4 or 5 years to gain new capabilities. No clue on cost, but it is a hardware module and software upgrades. Don't know if they have officially stated prices or exactly what will be there, but I watched a video from samsung on this and it seems like a cool ability. But of course you are limited to the screen's ability from a standpoint of resolution and so forth.
There may be something else, but those were the core things when I did comparison on Samsung site and watched a video from Samsung about their TV.s