If you are going to limit the 5th Party system to the first half of the long 1930s-1990s period of overlapping realignments (which is pretty reasonable), then the 6th Party system should be the second half of that period, and the period from about the end of the Clinton Administration on should be the 7th Party system; you can call now the 6th Party system if you call the entire long realignment period the 5th (which makes some sense, too, though there is a pretty significant difference between the New Deal dominant period and the Civil Rights dominant period of the realignment), but to split it somewhere in the middle but then lump the period after with it makes little sense.