Especially in the case of a character, microdetail should be added using a Normal Map. There's no such a thing like microdisplacement in Octane right now.
Texture Displacement should never be used for characters, and especially for deforming mesh. For that, you need to use Vertex Displacement.
Its' very important to set the gamma for the Displacement Map you're using to 1, and change the depth (16 or 32) to the one supported by the file.
Vertex Displacement allows to get some very nice detail without the need of subdividing the base mesh too much. Autobump can really help showing the full detail the map offers.
I've made a quick test to show the power of Vertex Displacement with AutoBump.
Mesh subdivided 4 times, 12 million polygons:
Mesh subdivided 3 times, 7 million polygons:
Mesh subdivided 2 times, 7K polygons:
Can you really spot so much difference when you're looking at one image at time? Moreover, of course there's no normal map in those images, which is something you normally export from ZBrush when working with sculpted characters.