I have been looking at those as well. For the $$, the 6000 is not a bad deal but depending on the room, and the "necessity" of a true black, then you might want to go with the 8500 in order to get the local dimming.
However, for a cheaper alternative to the 8500 - Check out the Vizio 55" VF551XVT. Has the same options as the Samsung 8500, however it is not as thin, still has the local dimming, and is 1/2 rhe cost of the Samsung.
(I think I may be going with the Vizio)
Best of luck.