Nice sculpt! And thanks for sharing your workflow from 3DCoat to C4D/Octane. I too have been trying to optimize my workflow to C4D/Octane and am not yet satisfied. The default Octane preset just does not look right in C4D/Octane. Specifically the metal materials. I'm not 100% sure I'm even setting up the C4D/Octane material correctly. Figured I'd reach out to see what your process is.
First off, when painting, which 'texture export/import workflow' are you using? I think this can be toggled anytime, but figured I'd check. I've been using (the default?) metal/rough workflow, as it aligns with my Unity work. (Unity export preset looks fantastic in-game...just can't get the same thing in C4D/Octane)
Exporting out of 3DC with the default Octane preset (using metal/rough workflow), I get:
Albedo color (RGBa)
In Cinema, I create new Octane Glossy Material, and add 'c4doctane > image texture' to the color slot and add the albedo. Then another image texture in the specular slot and add the Metalness map from 3DC. Then another image texture in the roughness slot and add the roughness map from 3DC. Finally, another image texture in the normal slot and add the normal map from 3DC.
The color and normal seem fine, but the metal looks nothing like what I get in 3D Coat. I've loaded the exact same HDR in both C4D/Octane and 3DC, but not even close. Screenshots attached for reference.
Let me know if you have any thoughts. And keep up the great sculpting work!