The difference is that the UN55C8000 has an additional 2M:1 Dynamic Contrast Ratio, moving from the C7000's 6M:1 to 8M:1.
It also incorporates the Precision Dimming feature, which allows certain parts of the screen to dim in darker scenes than other parts. This feature isn't available on the C7000.
Also, the design of the unit is different, so you might look for yourself at which design you prefer.
Does that help?
What is the difference between these 2 3D LED-LCD TV's?
They are about $300.00 different in price.