Helicenes

In the flat compounds, from phenanthrene to the compound with ten rings, each extra ring contributes 18.0 - 18.4 kcals to the HoF (black line in plot below).
In the helical structures this increment is larger, but also rather constant: about 24.5 kcal (red line).
In the symmetric C_s structures (blue line), the increment is initially very large: 38.5 from [4] to [5], but it drops to 25.8 from [7] to [8], and then just below the helix value: 23.8 from [8] to [9], 24.2 from [9] to [10]. The blue and red lines run more or less parallel here.
From [10] onwards, the C_s structure and the racemization transition state (TS) do not coincide anymore.

It can be expected, based on the 'sheep horn' effect, that the C_s structures for [11], [12], etc. will be significantly higher in energy than for [10]. Moreover, they will be local maxima, on interesting, 'bumpy' energy profiles. This makes a nice subject for a computational chemistry lab.
However, one can imagine that the barrier levels off again for very long helices. Construct the 'helix-inversion-fold' in your telephone cord and move it from end to the other end. All these structures have the same enthalpy, and maybe somebody can explain what the role of entropy will be.