Hi,
I think you ask too much to the Octane's displacement. Cinema 4D has access to the information of the internal smoothing system of the sculpt subdivision module. The displacement channel of Cinema 4D renderer is then adapted to the sculpt baking. This is not the case of Octane then you should give a little bit more informations by baking your sculpt from a higher level than zero with "keep higher level" checked (by sample level 3 or 4).
I think the baking result is far better with my old Mudbox 2011 than with my old Cinema 4D R14, probably because even with a higher level mesh the C4D smooting is still a problem. Maybe it's better with a newer release of C4D, i don't know. And Octane seems to handel curioustly 32 bits floating point files (i'm unable to restore negative values of the file, only positive values) then i've found the result is far better with 16 bits files "centered" at this time.
Sorry for my poor english. Here a sample from Mudbox in C4D:
Here a screen capture of the Mudbox sculpture: