What was the last election of the 5th party system/first election of the 6th?

[Skill and Chance]

Not in favor of realignment theory in general, but to the extent there are very lasting trends, I would focus more on who the parties appealed to vs. how well they did in a particular set of elections:

1896-1948: Industrial laborers overtake farmers, rise of organized labor/social class based politics, Dems begin building a new base, end of the Civil War era.  At first it seems odd to group the 3 consecutive Republican landslides together with 4 consecutive Democratic landslides, but FDR was really just a supercharged version of the Bryan coalition.

1952-1988: The suburbs become politically significant for the first time, New Deal reforms firmly entrenched despite one-party Republican rule, the former laborer class feels economically secure for the 1st time.

1992-present: For the first time, the Democrats win by reaching out to suburban managerial voters.  Republicans work to build a rural base surprisingly quickly.   

IMO, it's hard to argue that we aren't still living in the post-1992 era.