Firstly, I would argue that Hertl is a top-6 forward, and I would say Ward is a 2nd/3rd line tweener rather than a true top-sixer.
And I would also agree in that we have four 1st liners.
Just my opinion:
1st liners: Thornton, Marleau, Pavelski, Couture
2nd liners: Hertl
2nd/3rd line tweeners: Ward
3rd liners: Donskoi, Karlsson (borderline)
4th liners: Tierney, Nieto, Wingels, Smith, Zubrus, Goodrow
Non-NHLers: Brown, Lerg, Haley, etc.
Ideally IMO, you pair a couple of first liners (JT/Pav and Patty/Logan) with a tweener (Karlsson/Ward), for a couple of decent first lines. You have an extra 2nd line center (Hertl) and you give him a couple of third liners (Donskoi/Aquisition), and then make up a fourth line of actual NHLers: a line of Nieto-Tierney-Wingels would be a high-end fourth line capable of playing in both ends, not being liabilities, playing on the PK to eat minutes, and chipping in a goal every once in a while.
(In giving these "categories" of sorts, I mean specifically on a playoff team.)