The models improve a little every year. For the "C" models, this year the 8000 Series offers 3D, a darker black filter (for better dynamic contrast ratio) and Motion Judder control to improve the smoothness of the picture. There's also an additional calibration mode if you decide to have your set calibrated.
Also, the PN50C8000 also comes with Samsung Apps, which is a whole new offering of widgets and additional features. You can check those out here:
Does that help answer? If you have more questions, I'll be happy to assist.
Just wondering what is the difference between the 50 inch B850 and the 50 inch C series (several)? Which is "better"?
Price comparison wise, the C series look cheaper..
Also what would be a good price range for the PN50B850 used? $1100? $900?