It seems that samsung has tried to create new lines that matched their old lines.
xx42 -> series 3 (6 ms, 720p, 8000:1)
xx53 -> series 4 (6 ms, 720p, 10000:1)
xx61/65 -> series 5 (5 ms, 1080p, 30000:1)
xx71 -> series 6 (4 ms, 1080p, 50000:1, 120 hz)
series 7 is somewhere above xx71, but so far unsure if its like the xx81, or if that will be replaced by the "series 9", and this is only an upgraded 6.
those are the basic features, its obviously more complex than that.